HISTORICAL NOTES ON THE USE OF AIR POWER AS A WEAPON OF INTERDICTION

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78S02149R000100030003-4
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 42
• Document Creation Date: November 16, 2016
• Document Release Date: March 13, 2000
• Sequence Number: 3
• Publication Date: May 1, 1966
• Content Type: IR

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Copy No. 89
CIA/RR ER 66-8
May 1966
INTELLIGENCE REPORT
HISTORICAL NOTES ON THE USE OF AIR
POWER AS A WEAPON OF INTERDICTION
DIRECTORATE OF INTELLIGENCE
*USAF Declass/Release Instructions On File*
GROUP 1
Excluded from automatic
downgrading and
SE7~; T decl on
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This material contains information affecting the Na-
tional Defense of the United States within the mean-
ing of the espionage laws, Title 18, USC, Secs. 793
and 794, the transmission or revelation of which in
any manner to an unauthorized person is prohibited
by law.
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FOREWORD
Prior to the current operations in Vietnam, the United States was
engaged in three wars in which air power played a major role as a
means of conducting offensive warfare. This report summarizes the
role of air power in-the air wars against Germany, Japan, and North
Korea. The analysis of the air wars against Germany and Japan
treats in general terms the overall economic effects of the campaign,
with somewhat more detailed treatment of the attacks on transporta-
tion. The air war against Korea is most similar to the air war being
conducted in North Vietnam. For this reason the Korean War is
examined in greater detail to evaluate the attempts to interdict North
Korea's transport system.
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CONTENTS
Page
I. The Air War Against Germany .............. ........... 1
A. The German Economy 1
B. Overall Economic Effects of Bombing ............... 2
C. Target Systems .................................... 3
1. Civilian Morale ................................. 4
2. The Attack on the Ball-Bearing Industry ............ 5
3. The Aircraft Plants as a Target System .............. 5
4. The Attack on the Petroleum Industry .............. 6
D. The Attack on Transportation ........................ 7
1. Inland Waterways ............................... 8
2. Railroads ....................................... 8
II. The Air War Against Japan ............................. 11
A. The Air Attacks Against Japan Proper ................. 11
B. Effects of the Attacks 12
C. Civilian Morale .................................... 12
D. Destruction of Japanese Merchant Shipping ............ 13
E. Actions of the Elite to End the War ................... 15
III. The Air War Against North Korea ....................... 17
A. Introduction ....................................... 17
B. Similarities and Differences of Environment ............ 17
C. Interdiction in North Korea .......................... 17
1. Introduction .................................... 17
2. Railroad Interdiction-Operation Strangle .......... 21
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Page
3. Evaluation of Operation Strangle .................. 23
a. Introduction ................................. 23
b. Railroad Interdiction .......................... 24
c. Highway Interdiction .... .................... 24
d. Night Operations .............................. 25
e. The Wa-d.ong Chokepoint ...................... 26
D. Strategic Bombing ................................. 27
1. Early Bombing ................................. 27
2. Later Strategic Bombing Efforts ................... 29
a. Hydroelectric Power .......................... 29
b. Irrigation Dams .......... .................... 29
E. Lessons from the Korean War ........................ 30
1. Introduction .................................... 30
2. Failure of the Interdiction Campaign ............... 30
3. Air Pressure Tactics and Psychological Warfare
...... 32
4. Lessons for Vietnam
33
TABLES
Page
1. Distribution of Bomb Tonnages in the European Theater
During World War II ................................. 3
2. Comparison of Air Operations in Korea and North Vietnam ... 19
3. Strategic Targets Attacked in North Korea, 1950 ............ 28
CFIARTS
Follows Page
Figure 1. Effect of Allied Bombing on Gennan Munitions Pro-
duction ....................................... 33
Figure 2. Effect of Allied Bombing on Japanese Munitions Pro-
duction and Maritime Shipping ..... . ............
33
Figure 3. Indexes of Bombs Expended and Value of Destruc-
tion in the Korean War During Operation Strangle ..
33
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HISTORICAL NOTES ON THE USE OF AIR POWER
AS A WEAPON OF INTERDICTION*
1. The Air War Against Germany
A. THE GERMAN ECONOMY
The German war economy benefited greatly from the German
buildup in industrial activity which took place between 1933 and
1939. While both England and the United States entered World
War II with substantial unemployment, the German labor force was
fully employed by 1939. Six years of rising output (1934-39) meant
that substantial investments were made in expanding plant facilities,
both for heavy industry and for armament production. One result
was that the German armament industry, with -few exceptions, worked
only single shifts throughout the war and the great reserve capacity
available from double or triple shift operations not only gave con-
siderable flexibility but also cushioned the effects of Allied air attacks.
In 1938, approximately 30 percent of the national product was already
devoted to war expenditures, and this level rose very slowly until,
by the end of 1944, approximately 50 percent of the national product
was channeled into war purposes.
The output of civilian consumption goods, after the restrictions in
the initial war years, was reasonably well maintained so that civilian
standards of living continued to be, comfortably above the levels of
the depression years of the early 1930's.
Germany's dependence on imported raw materials was always looked
upon as a classical weakness in wartime. The four-year plan of
1936 was aimed in part at overcoming the most serious of these weak-
nesses, chiefly through expanded production of synthetic oil, textiles,
and rubber. However, Germany imported very substantial percent-
ages of iron ore, copper, manganese, and other metals. Partly as a
result of overrunning other Western European sources of supply and
*This report was prepared by the Office of Research and Reports; the estimates and
conclusions represent the best judgment of the Directorate of Intelligence as of 15 April 1966.
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partly as a result of substitution, Germany managed until well into
1944 to avoid serious embarrassment from shortages of imported war
material. The Germans found that consumption of many materials,
such as copper, traditionally believed to be essential to armaments
production, could be drastically cut without materially affecting the
quality or the usefulness of the end product.
While electric power supplies became tight early in the war, ra-
tioning and curtailment of nonessential uses permitted priority needs
to be met until .1944. During that year, certain major industrial
consumers, such as aluminum producers, were deprived of supplies
from time to time on a temporary basis.
In summary, the German economy proved surprisingly able to
withstand substantial attacks and still increase munitions output until
the weight of Allied bombardment: increased to approximately 300,000
tons a quarter, which did not take place until late in 1944 (see
Figure 1).
B. OVERALL ECONOMIC EFFECTS OF BOMBING .
During 1942 and 1943 the overall effects of air raids on the German
economy were small. The US Strategic Bombing Survey estimated
that the total loss of German armament production resulting from
air attacks carried out in 194:3 was not more than 3 to 5 percent, even
though the attacks required the Germans to call upon some of their
reserves.
In the first four months of 1944 the US air forces concentrated their
effort on aircraft plants and on antifriction bearing factories. The
vulnerability of these targets proved smaller than had been expected.
In May and June of 1944 the weight of attacks on Germany was
reduced because of the diversion of a high. proportion of the Allied
air forces to preparation for the invasion that was launched on 6 June.
The air offensive that started later, beginning with attacks on oil
and nitrogen facilities and continuing against German transportation,
achieved more noticeable results. Before the end of 1944 the output
of aviation gasoline and nitrogen had fallen by 90 percent. The
attack on transportation was a major factor in reducing the volume
of car loadings by 75 percent within five months. However, the index
of armament production stayed high. It reached a peak in the third
quarter of 1944; the decline in the fourth quarter (from causes other
than those attributable to territorial losses) was only about 5 percent.
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The Allied bombing program did succeed in tieing up a significant
portion of the labor force by the third quarter of 1944. An estimated
41/-, million workers, or nearly 20 percent of the nonagricultural labor
force, were engaged in debris clearance, reconstruction and dispersal
projects, the replacement of goods lost through air raids, and in the
manning and production of antiaircraft munitions. Air raid casualties
reduced the labor force by no more than 500,000 to 700,000, or about
2 percent.
From December 1944 onward, all sections of the German economy
were in a rapid decline. This was due to the results of bombing
in combination with other causes, particularly the military reverses
which had led to the invasion of Germany itself. In February 1945,
Silesia and the Saar had been lost, and car loadings were only 11 per-
cent of normal and still falling. The final land actions carrying the
Allied armies across the Rhine and Oder Rivers were under way by
the time the economy of Germany had ceased to be able to support
significant military operations.
C. TARGET SYSTEMS
The greatest weight of Allied air attack, approximately 56 percent,
was delivered against two target systems-land transportation and in-
dustrial areas (see Table 1). Transportation targets are discussed in
D, below.
The attacks against industrial areas, generally identified as city area
raids, were primarily the work of the Royal Air Force. It began its
famous raids on German urban areas in 1942, with the first thousand-
plane raid against Cologne. This was followed by heavy attacks on
other industrial cities, the most noteworthy of which were the July
Distribution of Bomb Tonnages in the European Theater
During World War II
PERCENT
Land transportation targets ........................................... 32.1
Industrial areas ..................................................... 23.7
Military targets ..................................................... 11.1
Oil, chemical, and rubber targets ...................................... 9.3
Airi~ields and airdromes .............................................. 6.9
Naval and water transportation targets ................................. 4.2
V-weapon launching sites ............................................. 2.0
Aircraft factories ................................................... 1.8
Miscellaneous manufacturing targets .................................... 2.6
All other targets .................................................... 6.3
Total ........................................................... 100.0
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and August strikes against Hamburg. The Hamburg raid destroyed
about one-third of the residential housing and killed between 60,000
and 100,000 people. While this raid had an immediate shock effect,
the city attacks prior to the autumn of 1944 did not substantially affect
German war production. I ecovery was essentially achieved within
a relatively few weeks, and because industrial plants were generally
located around the perimeter of German cities, they were charac-
teristically undamaged.
The heavy tonnages of bombs dropped on urban areas as a result
of attacks on transportation and targets beginning in September 1944
produced more significant effects. However, since there were so
many forces contributing to the collapse of production in the last six
months of the war, it has not been possible to assess separately the
effect of these later area raids on war production.
1. Civilian Morale
The conclusions of the US Strategic Bombing Survey with respect
to the effect of Allied air attacks on German morale are as follows:
The Survey has made extensive studies of the reaction of German
people to the air attack and especially to city raids. These studies were
carefully designed to cover a complete cross section of the German
people in western and southern Germany and to reflect with a minimum
of bias their attitude and behavior during the raids. These studies
show that the morale of the German people deteriorated under aerial
attack. The night raids were feared far more than daylight raids. The
people lost faith in the prospect of victory, in their leaders and in the
promises and propaganda to which they were subjected. Most of all,
they wanted the war to end. They resorted increasingly to "black radio"
listening, to circulation of rumor and fact in opposition to the Regime;
and there was some increase in active political dissidence-in 1944 one
German in every thousand was arrested for a political offense. If they
had been at liberty to vote themselves out of the war, they would have
done so well before the final surrender. In a. determined police state,
however, there is a widle difference between dissatisfaction and expressed
opposition. Although examination of official records and those of in-
dividual plants shows that absenteeism increased and productivity di-
minished somewhat in the late stages of the war, by and large workers
continued to work. However dissatisfied they were with the war, the
German people lacked either the will or the means to make their dis-
satisfaction evident.
The city area raids have left their mark on the German people as
well as on their cities. Fair more than any other military action that
preceded the actual occupation of Germany itself, these attacks left the
German people with a solid lesson in the disadvantages of war. It was
a terrible lesson.
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2. The Attack on the Ball-Bearing Industry
The classic example of an attack on a so-called bottleneck industry
was that of the German ball-bearing industry. Not only was ball-
bearing production concentrated, with approximately one-half of the
output coming from plants in the Schweinfurt area, but also Germany
was assumed to need a continuing full supply of ball bearings to
continue war production.
Air attacks on Schweinfurt took place on 17 August and 14 October
1943. Losses to attacking German fighters (the plants were outside
of escort range) were such that the attacks could not be maintained.
During the next four months, when there was a bombing lull, the
Germans took energetic steps to disperse the industry. This dispersal
was aided by the fact that machine tools were relatively undamaged.
Furthermore, it proved possible to eliminate very high percentages
of the total number of ball bearings used in some equipment without
materially impairing its operation for either civilian or military pur-
poses. The Germans had also exercised the precaution of accumu-
lating substantial stocks. From examination of the records in the
ball-bearing industry, and from the testimony of war production
officials, there is no evidence that the attacks on the ball-bearing
industry had any measurable effect on essential war production.
3. The Aircraft Plants as a Target System
The abortive experience with the ball-bearing industry was followed
by renewed attacks on the German aircraft industry. Earlier attacks
had the effect of reducing the vulnerability of aircraft assembly plants
because the Germans pursued a policy of subdividing and dispersing
aircraft production facilities. The new attacks began in February
1944, with the protection of long-range fighter escorts, and were
again aimed at aircraft assembly plants as opposed to aircraft engine
plants. These attacks did not succeed in reducing the production of
aircraft, probably because there was considerable excess capacity in
the assembly phase of the aircraft industry and because, once again,
relatively simple protective measures prevented serious loss of machine
tools. Hence the attack on the ball-bearing industry and the attack
on aircraft assembly facilities were proved to be errors in target se-
lection. The German Air Force was defeated, but its defeat came
largely as a result of combat operations by the Allied forces. Later
in the war the Ruhr steel industry was singled out as a target system,
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but because steel lies so deep in the industrial process there is no
evidence that these attacks affected munitions production before the
end of the war.
4. The Attack on the Petroleum Industry
The attack on the German petroleum industry began in a pre-
liminary way with two strikes in May 1944. These attacks were
not followed up, because of the almost complete diversion of air
power to attacking tactical targets in preparation for and in support
of the D-Day invasion.
The German oil position was tight throughout the war, and
production was largely concentrated in 13 synthetic fuel plants.
Although there were early attacks on the Rumanian petroleum in-
dustry, by August 1944 this source of supply was overrun by the
USSR, and German dependence on the synthetic plants became almost
complete.
By July 1944, every major plant had been hit. After the attacks
began in May, production, which had averaged 316,000 tons per
month, fell to 17,000 tons a month in September. Although there
was a modest recovery in November and December, the post-attack
output was only a fraction of the pre-attack level. Unlike the ball-
bearing plants, the synthetic oil plants were attacked again when
they were brought back into operation. For example, the largest
plant, Leuna, was attacked 22 times by early 1945, and its output
from the day of the first attack averaged only 9 percent of capacity.
The effects of depriving Germany of its major fuel resources were
almost immediate in terms of military operations. For lack of fuel,
pilot training was drastically curtailed, making German aircraft in-
creasingly vulnerable to experienced Allied fighters. As the summer
of 1944 wore on, the German panzer divisions were more and more
seriously hampered by decreased fuel production.. German military
stocks of petroleum were so low that when the famous Ardennes
offensive (the so-called Battle of the Bulge) was launched, German
reserves of fuel were insufficient to support the operation. The
German high command counted. on capturing Allied stocks to keep
the operation rolling. Finally, in February and March of 1945 the
Germans massed 1,200 tanks on the Vistula to check the Russian
advance. In very short order, the tanks were overrun because they
had insufficient fuel for maneuver.
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There were other dividends from the attack on the petroleum in-
dustry because 60 percent of the nitrogen and 40 percent of the
methanol output came from the synthetic oil plants. Shortages of
these essential chemicals for munitions were reflected in shortages of
ammunition within a few months.
D. THE ATTACK ON TRANSPORTATION
The German transportation system was dominated by the rail-
roads. In combination, the state-owned and privately owned rail-
roads handled three-quarters of all freight traffic and about 70 percent
of passenger traffic. Most of the remainder of the freight traffic was
accounted for by waterway (largely inland) carriers and less than
3 percent by highway vehicles. The rigid government regulation
of trucks was designed to prevent the development of a highway truck
system which would compete with the state-owned railways for long-
haul business. Therefore, motor transportation was almost entirely
limited to local and suburban service.
The rail system was well maintained and had general- overcapacity
on permanent way, with respect to both lines and classification yards.
The inland waterways system connected the important rivers of North
Germany; crisscrossed the Ruhr coal area, and provided through water
transportation from the Ruhr into the Berlin area. The moderate
expansion of the rail system during the war was concentrated in those
few places where it was necessary to construct new yards in critical
points such as Munich or to parallel vulnerable viaducts with by-
pass lines.
During most of the air war against Germany the bombing of rail
transportation was not given a high priority. Although heavy major
ground operations were preceded or accompanied by concentrated
attacks on local rail facilities in or near the battle area, transportation
was not then selected as a priority target system, because of its size
and complexity. As a consequence, the railroads in Germany and
the ports of the inland waterways system were subject to only sporadic
attacks until the middle of 1944. Heavy attacks on transportation
within Germany proper did not begin until September 1944. The
recuperative powers of the system were such that until bomb tonnages
exceeded 12,000 tons per month the repair system was able to cope
with the damage.
At the same time that the heavy attacks were beginning on the
railroads, successful attacks on four waterway targets substantially
eliminated through traffic on the Rhine and North German canals.
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By 14 October the Rhine River was similarly interdicted at Cologne,
and as a consequence the economic traffic of the important Ruhr
district fell to about 12 percent of the level of October 1943-March
1944. By the end of December, car loadings had been decreased by
about 40 percent and by the first week of March 1945 by almost 80
percent. The index of munitions production held up substantially
better than these figures would indicate, largely because of stocks
of components and subassemblies.
1. Inland Waterways
The general experience with the attack on waterways was that
these were relatively successful in halting traffic-often for a con-
siderable period of time. Furthermore, there were frequent additive
side effects such as that resulting from the mining of the Danube River.
The period of intensified mine laying in the Danube was from April
to December 1944. The mines (and other aerial attacks) resulted
in the sinking of over 40 percent of the Danube cargo fleet. Further-
more, there was a precipitous drop in morale because mine explosions
often resulted in the loss of the crew. Consequently, desertions and
delays because of manpower shortages were numerous. The tonnage
handled on the river dropped about 60 percent within two months and
continued to fall throughout the summer. Complete statistics are
not available, but the Danube operation was clearly a highly
successful one.
2. Railroads
The bomb tonnages dropped on land transportation targets
Germany were as follows, by quarter:
1944
January-March .................................................
1,650
April-June ....................................................
8,250
July-September .................................................
19,200`
October-December .............................................
71,000
1945
January-March ................................................. 105,000
` Of which 13,000 tons were dropped in September.
It can be seen from the above figures that until September 1944
the tonnages dropped were not sufficient: to overwhelm the capa-
bilities of the repair system. Following that date the weight of the
attack increased sharply and. in the first quarter of 1945 was. 64 times
that of the first quarter of 1944. The result was a progressive tieup
of traffic.
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Although coal traffic (about 40 percent of all the traffic carried by
the German railroads) held up better than miscellaneous commercial
traffic, the decline was both more easily traceable and more dramatic.
The September raids reduced coal-car placements in the Essen Divi-
sion of the Reichsbahn (the originator of most of the coal traffic
of the Ruhr) to an average of 12,000 cars daily, compared with
21,400 at the beginning of the year. Most of this was for consumption
within the Ruhr. By January, placements in the Ruhr were down to
9,000 cars a day, and in February 1945 virtually complete interdiction
of the Ruhr District was achieved. The German economy was
powered by coal and, except in limited areas, the coal supply had
been eliminated.
Military (Wehrmacht) traffic had top priority over all other traffic.
During the period of attack this traffic came to account for an ever-
increasing proportion of the declining movement. Through 1944 the
air attack did not prevent the army from originating such movements,
although the time of arrival, or even the arrival, of units and equip-
ment became increasingly uncertain. Couriers accompanied detach-
ments and even shipments of tanks and other weapons; their task was
to get off the train when it was delayed and report where it could be
found. After the turn of the year, even military movements became
increasingly difficult. The Ardennes counteroffensive, the troops and
equipment for which were marshaled_ over the railroads, was prob-
ably the last such major effort the Reichsbahn would have been ca-
pable of in the West.
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II. The Air War Against Japan
At the outset of World War II the Japanese economy was relatively
small, approximately 10 percent the size of that of the United States.
Despite great efforts to increase the availability of raw-materials from
domestic sources, Japan was highly dependent on imports to main-
tain its industrial plant. The acquisition of Manchuria and parts of
China helped materially in alleviating Japan's shortages of coking
coal, iron ore, and foodstuffs, but negligible quantities of iron ore and
bauxite were available within Japan's "inner zone." Plans to develop
a synthetic oil industry failed to yield significant results, and Japan
was almost wholly dependent on imports from the Dutch East Indies.
The same overseas dependence existed for rubber, ferroalloys, and
manganese as well as for a variety of other militarily important ferrous
and nonferrous materials.
Japan's strategy had been based on the accumulation of munitions,
oil, aircraft, and ships which could be thrown into action against es-
sentially nonmobilized enemies. The expectation was that the dev-
astation of the initial blow would result in the enemy suing for peace.
A. THE AIR ATTACKS AGAINST JAPAN PROPER
Most of the tonnage of bombs dropped by Allied forces in the
Pacific War fell outside the Japanese home islands. Only one-fourth,
or 160,000 to 170,000 tons, was dropped on Japan proper, mostly by
B-29's. In contrast, 1,360,000 tons were dropped within Germany's
own borders. The air attack on Japan came very late in the war
and was very highly concentrated. From June 1944 to January 1945,
only 800 tons of bombs were dropped by China-based B-29's on the
Japanese home islands. Following the seizure of the Mariannas in
August 1944, a series of bases for long-range bombers were constructed,
but the tonnage dropped by 9 March 1945 totaled only 7,180 tons.
The basic revision in the method of B-29 attack came on 9 March
1945, when it was decided to bomb the four principal Japanese cities
at night with incendiaries. The first attack burned out 15 square
miles of Tokyo's most densely populated area. This enormously
destructive attack was followed almost immediately by strikes on
Nagoya, Osaka, and Kobe. In the aggregate 104,000 tons of bombs
were directed at 66 Japanese urban areas, or about two-thirds of the
total tonnage dropped on the home islands. Far smaller tonnages
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were directed against selected industrial and military targets, as fol-
lows : 14,150 tons against aircraft factories, :[0,600 tons at oil refineries,
4,708 tons against arsenals, 3,500 tons against miscellaneous industrial
targets, 8,150 tons at airfields, and 12,054 mines used in the attacks
against shipping.
B. EFFECTS OF THE ATTACKS
The physical destruction resulting,, from air attacks on Japan was
approximately the same as that suffered by Germany. The attacks
were more concentrated in time, and the target areas in Japan were
smaller and more vulnerable. Japan's defensive capabilities were
overwhelmed as was its will and capacity for reconstruction and dis-
persal. Some 40 percent of the built-up area of the 66 cities attacked
was destroyed, and about 30 percent of the entire urban population
lost their homes. Total civilian casualties as the result of nine months
of air attack, including an estimated 200,000 from the atomic bombs,
were approximately 806,000. These casualties probably exceeded
those which Japan suffered in combat.
The economic effects of the air attacks are difficult to specify be-
cause the loss of merchant shipping had essentially isolated Japan
from its sources of industrial raw materials. Most of the oil refineries
were out of petroleum, the aluminum plants were out of bauxite, the
steel mills were short of ore and coke, and the munitions plants were
low on steel and aluminum. Japan's economy was in large measure
being neutralized twice over, first by cutting off imports and second
by air attack.
The railroad system was not subject to substantial attack and was
in reasonably good operating condition at the time of surrender.
Japan's electric power system had not been selected as a target sys-
tem, largely because it existed in numerous small production facilities.
Therefore, most of Japan's generating and distribution capacity re-
mained operable. An exception was in the urban areas which had
been subject to heavy incendiary attack.
C. CIVILIAN MORALE
The early Japanese military successes, particularly the capture of
Singapore, were followed by a wave of optimism and high confidence
on the part of the Japanese people. As the war progressed, subse-
quent defeats were studiously withheld from the people or disguised
as strategic withdrawals. The US Strategic Bombing Survey reported
that as late as June 1944, in spite of an increasing shortage of food
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and exhausting work to support the war effort, only about 2 percent
of the Japanese population believed that Japan faced the probability
of defeat. The beginnings of attacks on the home islands coupled
with military defeat in the Philippines and a continuing deterioration
of food supplies began to be reflected in sharply lowered civilian
morale. The survey reported that by June of 1945 nearly one-half
of the Japanese people believed that victory could no longer be
achieved. One striking effect of air attack on the cities was the mass
evacuation which resulted. Roughly one-fourth of the urban popula-
tion either fled or was evacuated. Progressive lowering of morale
was characterized by loss of faith in military and civilian leaders,
loss of confidence in Japan's military might, and increasing distrust
of government news releases. The interrelationship of military, eco-
nomic, and morale factors was a complex one, in which the urban at-
tacks had played an important role. It should also be remembered
that the effect of the atomic bomb was severe not only on the civilian
population but also on the civilian and military leadership.
D. DESTRUCTION OF JAPANESE MERCHANT SHIPPING
Japan's merchant fleet was a key link in supplying home industry
with raw materials as well as being vital to the support of armed
forces in the field. Approximately 9 million tons out of a total avail-
ability of 10 million tons of merchant shipping (including ships of 500
tons and over) was sunk or seriously damaged during the war. About
55 percent of this loss was from submarines and approximately 10
percent from mines, most of which were dropped by aircraft. Most
of the remainder fell victim to direct air attack. Thus the role of
airpower in the isolation of the Japanese home islands was a major
one, even though it was secondary to that of the submarine (see
Figure 2).
As a maritime nation with large domestic and foreign trade, Japan
had developed a modern merchant marine of first rank. Because
shipping was highly developed and heavy industry was located to use
fuel and raw materials received by water routes, the railroad mileage
was small and the rail system of ? limited capacity. Only two main
rail lines extended the length of Honshu Island. The fleet of large
oceangoing ships was complemented by numerous smaller craft en-
gaged in the coastal trade in and around the home islands..
The conquest of Southeast Asia gave Japan control of most of the
world's supply of rubber, tin, antimony, jute, and quinine as well as
sources for more than enough of its own requirements of petroleum,
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iron ore, bauxite, sugar, corn, and rice. During the war, Japan drew
heavily on this area for the bulk raw materials needed by its industry.
Despite a vigorous building program, Japan after 1942 was not
able to maintain the prewar level of total tonnage of merchant ships
afloat. The December 19411. level was 5.4 million tons of merchant
ships, excluding tankers. A. year later, this total had been reduced
to 5.2 million tons, and by December 1943 the combination of sub-
marine and air attacks had lowered ship availability to 4.2 million
tons. The submarine offensive had been particularly stepped up in
the fall of 1943.
The year 1944 saw the beginning of the devastating carrier attacks
on merchant shipping, originally as a result of the carrier raids on
Truk and Palau. A series of operations involving the invasion of the
Mariannas and the preinvasion carrier raids around the Philippines
followed in the summer and the fall. Sorties against merchant ship-
ping flown by Army, Navy, and Marine land-based and carrier-based
aircraft increased from 118,000 in 1943 to 327,000 in 1944. In 1945
the combined sorties reached a monthly peak of almost 51,000 in
April. During 1944 the merchant tonnage afloat had been reduced
over 50 percent in a 12-month period and was only about 1.5 million
tons when Japan surrendered.
Other air operations had a significant effect in reducing the mobility
of the shrinking merchant fleet despite Japan's willingness to take
severe shipping losses because of its desperate need for strategic im-
ports. The mine-laying campaign conducted by the B-29's early in
1945 not only reduced the total tonnage of merchant shipping but also
blockaded certain ports and greatly reduced the serviceability of
others.
Oil imports passed their peak in August 1943. The Japanese Navy
had lost a significant number of its tankers at Truk, and further sink-
ings of tankers created desperate shortages of fuel by the fall of 1944.
By April 1945, tanker imports ceased completely. Stocks had been
drawn down and were quickly exhausted, the fuel supply for the
shipping industry began to dry up, and a considerable tonnage of
smaller ships was laid up by lack of etroleum. Despite the accumu-
lation of stockpiles of industrial raw materials, even the direct muni-
tions industries suffered serious losses in output as a result of the
interdiction of merchant shipping. For example, aluminum output
declined 76 percent in a single year as a result of the stoppage of
bauxite imports.
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Finally, the nation became short of food. Local production had
declined, partly as a result of cutting off imports of fertilizers. Fish-
ing, a major industry prior to the war, was reduced by 50 percent for
a variety of reasons, including requisitioning of ships by the Japanese
Navy and the shortage of fuel. The situation became so acute by
April 1945 that virtually all of the small remaining shipping capacity
was diverted to the import of food and salt, sacrificing the trickle of
industrial raw materials that had still been flowing in. By April 1945,
Japan was essentially isolated. The raw materials base of its economy
had been cut off, and the country could look forward only to gradual
starvation and increasing military impotence.
E. ACTIONS OF THE ELITE TO END THE WAR
Although in theory the Japanese Emperor was the sole authority, in
practice he usually approved the decisions of his advisers. During
the early years of the war these advisers were dominated by fanatical
army and navy officers. The first definite breach in the political coali-
tion did not occur until Japan's defeat at Saipan. Ten days later,
on 16 July 1944, the Cabinet headed by General Tojo fell.
Tojo's government was succeeded by one headed by General Koiso.
Despite the original instructions to the Cabinet to give "fundamental
reconsiderations" to the problem of continuing the war, Koiso was
unable to stand up to the more determined military officers. His
major accomplishment was setting up a Supreme War Direction Coun-
cil which was the inner cabinet group through which the problem of
surrender was eventually resolved.
The conviction and strength of the peace party was increased by
continuing Japanese military defeats after Saipan and by Japan's
inability to defend its airspace against attacks in late 1944 and early
1945. After the US landing on Okinawa in April 1945, General Koiso
was replaced by Admiral Suzuki.
In May 1945 the Supreme War Direction Council began active dis-
cussions on ways and means to end the war. The Council initiated
discussions with the Soviet. Union seeking mediation. On 20 June
1945 the Emperor on his own initiative called the Supreme War Direc-
tion Council together and ordered it to develop.a plan to end the war.
August brought the decisive steps, with the atom bomb falling on
Hiroshima on the 6th and the USSR entering the war on the 9th. The
Emperor quickly resolved the conflict in favor of unconditional sur-
render.
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In retrospect, it is clear that, at the highest levels within the Japanese
Cabinet, the movement to bring the war to an end began over a year
earlier than the date of the final surrender. Japan's surrender cannot
be imputed solely to any one of the numerous reversals which jointly
contributed to the final decision. The military reversals in the field;
the destruction of the Japanese fleet and. merchant marine, which
isolated the home islands; the surrender of Germany; the destruction
caused by incendiary and atomic weapons; and, finally, the Soviet
decision to enter the war, all. played a part.
16 SECRET
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III. The Air War Against North Korea
A. INTRODUCTION
The lessons learned in one war against an adversary using strategy
and tactics appropriate to the time and place cannot often be applied
with success to another war fought under different conditions. Im-
proved weapons alone can negate the lessons of an earlier war. Fur-
thermore, each war is unique in its total setting-the political and
economic realities of a North Vietnam are not those of a North Korea
any more than the tropical setting of the former is equal to the harsh
climate of the latter.
This section places particular emphasis on the attempts by US
aviation forces to interdict the transportation system and to destroy the
heavy industry of North Korea. In spite of the differences between
North Korea and North Vietnam, these aspects of US operations in
North Korea are relevant to current US air operations in North Vietnam.
B. SIMILARITIES AND DIFFERENCES OF ENVIRONMENT
Numerous similarities exist between the present war in Vietnam
and the Korean War. Each conflict involves a divided country. Com-
munist China looms over the northern border of both North Korea
and North Vietnam as a supplier of war materiel and as a participant
or potential participant. Many contrasts exist also. The topographic
and climatic settings of the military actions in South Vietnam are unlike,
those fought in Korea. Instead of the guerrilla and infiltration tactics
characteristic of today's war in South Vietnam, the Korean War even-
tually involved large-scale land armies.
Other contrasts can help put the two conflicts in perspective. North
Korea occupies an area of about 47,000 square miles and in 1953
had a population of 9 million; North Vietnam has an area of 61,000
square miles and a population of 18 million.
1. Introduction
In the summer of 1951 as talks about a truce began and the fighting
lulled, the US Eighth Army calculated that enemy forces in Korea
were stockpiling daily 800 tons of supplies behind their lines. It was
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feared that the enemy would "reach a degree of preparedness pre-
viously unparalleled in the Korean War." To interfere with this
buildup, the Far East Air Force (FEAF) planned Operation Strangle,
a comprehensive interdiction, campaign against North Korea's rail-
roads and highways.
Operation Strangle had two principal objectives: (1) the knocking
out of the North Korean rail system by maintaining continuing rail cuts
at numerous points and by destroying rolling stock and equipment,
and (2) the disrupting of rail services so that the North Korean and
Chinese Communist forces would have to use the highways, which
could be brought under effective attack, to transport most of their
military supplies.
Postmortems on Operation Strangle have claimed that the codename
was an unfortunate choice because it implied more than had. been
intended. Nevertheless, that name mirrors initial Air Force optimism
about the probable effectiveness of an interdiction program. For
example, one official statement at the beginning of Operation Strangle
claimed:
The Fifth Air Force and. attached units in conjunction with US
Naval Air units and FEAF Bomber Command have the capability
of destroying the enemy's rail system in North Korea, and of hin-
dering his highway transportation system to such an extent that
he will not be capable of opposing; the US Eighth Army effectively.
Starting in August 1951 and extending over the next 11 months,
81,600 interdiction and armed reconnaissance sorties were flown by
the USAF, and more than 104,000 tons of bombs were dropped during
the interdiction and armed reconnaissance sorties.* By contrast, in a
similar time period (February-December 1.965) in North Vietnam,
27,900 sorties were flown and 34,300 tons of bombs, napalm, and
rockets were expended against fixed and armed reconnaissance targets.
During Operation Strangle an average of almost 10,000 tons of bombs
were dropped monthly. The peak month for Rolling Thunder oc-
curred in December 1965 when 5,500 tons of bombs, napalm, and
rockets were expended. A summary comparison of air operations in
the Korean War and in North Vietnam. (Rolling Thunder) is presented
in Table 2.
* Because of its unfortunate codename, there was considerable controversy (during the
Korean War) about the timespan covered by Operation Strangle. The time limits used are
those contained in the official Air Force history. Thus Operation Strangle (later Operation
Saturate) began in August 1951 and Continued through June 1952.
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Sorties
Total ...........................
Total combatb ...................
Total interdiction and armed recon-
naissance?....................
Total combat expenditures
Bombs (tons) ....................
Napalm (tons) ...................
Rockets (rounds) .................
Expenditures for interdiction and
armed reconnaissance
Bombs (tons) ....................
Napalm (tons) ...................
Rockets (rounds) .................
Damage
Bridges
Destroyed .....................
Damaged .....................
Tunnels
Destroyed .....................
Damaged .....................
Locomotives
Destroyed .....................
Damaged .....................
Freight cars
Destroyed .....................
Damaged .....................
Railroad cuts ....................
Trucks and other vehicles
Destroyed .....................
Damaged .....................
Buildings
Destroyed .....................
Damaged .....................
Entire War
June 1950-July 1953
Opera
August
tion Strangle
1951-June 1952
Rollin
February-
g Thunder
December 1965
710,886
214,485
N.A.
461,554
144,724
N.A.
220,168
81,613
27,932 d
386,037
118,207
N.A.
32,357
4,313
N.A.
313,600
50,707
N.A.
218,448
104,115
3,815
2,192
34,261
97,885
30,492
1,153
223
161
3,049
763
432
65
41
N.A.
939
257
N.A.
963
272
6
1,171
345
6
10,407
3,638
227
22,674
7,069
592
28,621
24,251
N.A.
82,920
33,210
483
33,131
14,768
565
118,231
9,109
1,837
88,461
17,382
2,266
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KOREAN WAR.
Entire War Operation Strangle
June 195x July 1953 August 1951-June 1952
Damage (Continued)
Oil storage tanks
Destroyed .....................
Damaged .....................
Barges and boats
Rolling Thunder
February-December 1965
16 0 N.A.
3 0 N.A.
Destroyed ..................... 593 225 460
Damaged ..................... 821 284 753
Aircraft
Average inventory
Bombers, light..................
Bombers, medium ..............
Fighters .......................
Operational losses I
B-26 ...........................
B-29 ...........................
F-51 ...........................
F-80 ...........................
F-82 ...........................
F-84 ...........................
F-86 ...........................
192= 150h
118 a 103 h
1,511= 982 h
168 57
57 24
300 98
277 67
11 2
249 121
184 66
Excluding sorties flown by the US Navy and Marines and by other friendly forces. During the Korean War, Navy and
Marine aircraft flew 275,912 combat sorties: 204,99.5 offensive, 44,160 defensive, and 26,757 reconnaissance. Ordnance
expenditures were 178,399 tons of bombs and 274,189 rounds of rockets. Navy aircraft were heavily engaged in Operation
Strangle, but no specific data, comparable to USAF statistics, are available.
b Including close support, strategic, counter-air-offensive, counter-air-defensive, reconnaissance, and interdiction and
armed reconnaissance, but excluding combat support sorties such as rescue, cargo, and tactical control.
A mission with the primary purpose of penetrating enemy lines and destroying or damaging traffic, communications,
and movement significant to the enemy's military operation in a given area.
a Including 6,928 sorties against fixed targets and 17,129 armed reconnaissance sorties.
In addition, Navy and Marine aircraft destroyed during the Korean "far: 2,005 bridges, 391 locomotives, 5,896 freight
cars, 7,437 vehicles, and 44,828 buildings.
E Barracks, warehouses, and miscellaneous buildings.
Peak average inventory, April-June 1953.
i, Average inventory, July-September 1951.
In addition, 564 Navy and Marine aircraft were lost to enemy action between 25 June 1950 and 27 July 1953.
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Operation Strangle was not, however, the first US attempt at inter-
diction in Korea. In the first year of the Korean War the Air Force
had flown 70,000 interdiction and armed reconnaissance sorties out of
a total of 140,000 combat sorties, but the fluid military situation had
required that major emphasis be given to close support of combat
troops.
2. Railroad Interdiction-Operation Strangle
For the first three months, Operation Strangle was successful.
Major rail lines were disrupted, and fighter-bombers destroyed railroad
track faster than the enemy could rebuild it. By early October 1951,
rail movements ceased, even on the double-tracked line from the
capital of P'yongyang south to Sariwon just north of the battle zone.
By November 1951, virtually all direct major rail routes to Manchuria
had been severed, although limited serviceability existed by shunting
traffic inland and then back to either coastal or other interior rail lines.
Interdiction and armed reconnaissance accounted for more than 60
percent of all combat sorties from the start of Operation Strangle
through the end of 1951. The number of sorties flown and bomb
tonnages expended reached a peak in October, when 9,700 interdiction
and armed reconnaissance sorties were flown and more than 10,000
tons of bombs were dropped. In the first two months of Operation
Strangle, interdiction and reconnaissance targets claimed more than
90 percent of the total weight of bombs dropped.
These attacks reached a peak of destructiveness in September
through November 1951. In September, Air Force pilots alone
claimed the destruction of 38 locomotives, 558 freight cars, 5,400 ve-
hicles, and about 1,400 buildings. Rail lines were severed about
15,000 times.*
Immense damage was done to the transportation system of North
Korea, even when allowance is made for the exaggerated claims of
destruction. The first intense blows did not knock out the system,
however, and in the following months the serviceability of the North
* The official USAF Historical Study of Air Operations in the Korean War recognizes that
pilots' claims of vehicles destroyed were greatly exaggerated, the results of night attacks
being especially hard to evaluate or check. In September 1951 the Fifth Air Force issued
a directive permitting night intruders to claim enemy vehicles destroyed only when the vehicles
were seen to burn or explode. Yet even this requirement probably did not prevent multiple
claims. For example, North Korean truck drivers carried oily rags which were lighted when
they were under attack to feign destruction and be spared further attack. Eventually, claims
of locomotive "kills" were allowed only when attacks were made using 500-pound bombs or
larger and after which the locomotive was observed to be derailed or in at least three
separate parts.
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Korean transport system improved materially. Tonnages being moved
on the railroads and highways were only a small fraction of peacetime
"capacity," but the supplies getting through were more than sufficient
to support the Communist armies in the field. The North Koreans
and Chinese developed an increasing capability to repair damage from
air attacks and to get both rail and highway traffic moving again.
Repairs were being made so rapidly that by late :December 1951 the
Fifth Air Force recognized that "thee enemy had broken our railroad
blockade of P'yongyang and .... [has] won the use of all key rail
arteries."
In February 1952, Operation Strangle (renamed Operation Saturate)
was modified to reflect the lessons of the previous six months. Rail-
road interdiction was still emphasized, but attacks were concentrated
against specific pre-targeted segments of the rail line. The change
in air operations, and its successes and failures, can be seen in a de-
scription of one attack made against the rail line between Chongju
and Sinanju. In a leadoff attack in late March 1952, 307 fighter-
bombers dropped 530 1L,000?-pound bombs and 84 500-pound bombs.
The following day, 160 fighters dropped 322 1,000-pound bombs.
During the night, B-26's dropped 42 500-pound bombs on what had
already become a major gap in the rail line:. However, the ability of
the North Koreans to repair rail damage had further improved; within
six days the roadbed was almost completely rebuilt and the tracks
were replaced. The 48-hour attack and the expenditure of 450 tons
of bombs had interdicted the rail line for 6 to 7 days but had required
the commitment of almost the entire fighter-bomber force. At the
same time other rail lines had remained open.
In April 1952 a penetrating staff study by the Air Force recognized
that in spite of the vast damage inflicted the interdiction operation
had not achieved its objectives and that such operations were be-
coming more costly in terms of casualties to air crews and aircraft
lost and damaged. Furthermore, some of the most modern US weap-
onry was being effectively countered by hordes of unskilled labor and
minimum amounts of easily attainable materials.
Policy changes which emerged from, the staff study emphasized
the need to inflict maximum damage on the enemy and to mini-
mize US losses, and included some shifts in targets. Thus, while loco-
motives, motor vehicles, and other transportation targets were still
rated as prime targets, equal or greater emphasis was given to radar,
guns, supply depots, mines, powerplants, and military schools. In
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effect, the new targeting took account of economic principles. From
attempts to physically cut the rail and highway systems the attack
moved to inflict maximum damage upon the enemy's limited stock of
military and transport capital in North Korea, capital which could
not be replaced by the labor of unskilled peasants. Nevertheless, the
new attack policy, announced in July 1952, admitted that "obstruction
of enemy supply movement in Korea cannot prevent the enemy from
gradually building up his stockpile." Although the Air Force con-
tinued to bomb selected bridges and rail targets during the remaining
year of the war, Operations Strangle and Saturate were at an end.
3. Evaluation of Operation Strangle
a. Introduction
Operation Strangle and Operation Saturate failed to achieve their
major objectives not only because there was an insufficient number of
aircraft to maintain an adequate number of rail cuts but also because
enemy countermeasures were more successful than had been estimated.
Communist antiaircraft defenses increased markedly, and the Com-
munists showed an increasing ability to improvise repairs, to build
bypass lines, and to mass peasant labor to maintain and repair essen-
tial supply lines.
The decline in returns from Operation Strangle can be seen from an
analysis of bombs expended and damage achieved. During July 1951,
the month before Operation Strangle got under way, approximately
6,600 tons of bombs had been dropped on interdiction targets in North
Korea. Bombs expended increased sharply in August to 8,300 tons.
From August to September, bombs expended increased by about 2,000
tons, or one-fourth, and the estimated value of destruction increased
by about three times. After November, however, there was a steady
trend of diminishing returns from the bombing attacks despite a fairly
steady expenditure of bombs at an average rate of 9,800 tons per
month. As shown in Figure 3, the index of value of damage per ton
of bombs declined from a peak of 100 in September 1951 to 39 in
January 1952 and a low of about 26 in April and June.
The combination of decreasing returns from air attack and the
sustained capability of keeping supply lines open meant that the North
Koreans and Chinese in defensive positions were able to move in their
daily logistic requirements and to make significant additions to stock-
piles. They were, however, unable to mount a sustained offensive,
because of the supply ceiling imposed by air attack.
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b. Railroad Interdiction
During 1950-53 the North Korean rail system consisted of about
2,300 miles of line, largely standard gauge, and included approximately
1,800 bridges and 400 tunnels. During the initial stages of Operation
Strangle the Air Force engaged in a multiprong attack against bridges,
rolling stock, tunnels, roadbeds, and rails. Tunnels, used extensively
to protect trains and supplies in daytime attacks, proved in most
instances to be impossible to destroy. Bridges were difficult targets,
but were destroyed consistently.
After the interdiction campaign had been under way for several
months the enemy showed a rapidly increasing capability to restore
damaged bridges. Construction materials were being stockpiled near
key bridges even before US attacks. Simple bypass bridges were built
frequently in from 2 to 4: days. Rail cuts were repaired in from 2 to 6
hours. Priority was placed on getting a bridge back in partial opera-
tion so that some supplies could begin to flow again although traffic
might remain far below capacity levels.
The North Koreans and Chinese stationed railroad construction
troops along all main supply routes which were under attack. Units
of 50 troops were located at all major rail stations, and crews of 10
men were located every 4 miles along the route. In addition, rail
walkers spotted damage to the rail or roadbed. Nearby inhabitants
were recruited for common labor, and sometimes as many as 1,000
persons were used to repair a damaged section. At dark, experienced
railroad construction crews would move in and make the actual repairs
to the rail line. Furthermore, in portage-like operations, rail service
was maintained on very short stretches of unable track-as short as 11
miles-and freight was unloaded, carried around rail cuts or damaged
bridges, and then reloaded on another train.
c. Highway Interdiction
The road network in North Korea, originally developed by the
Japanese, had always been of secondary importance to the railroads.
Trucks had been used typically for short hauls and served as links be-
tween industrial and commercial centers and the major railroads.
North Korea's principal. highways roughly followed the major rail
routes from Manchuria southward. Altogether about 10,000 miles of
highways existed, at best surfaced with gravel or crushed. stone.
Although the major interdiction effort of Operation Strangle was
against the North Korean rail system, attacks against trucks were also
pressed, especially night: attacks led by B-26's. On one occasion, an
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Air Force wing reportedly sighted 3,800 motor vehicles and attacked
2,600 vehicles in one day. The Air Force claimed that 6,400 trucks
were destroyed in October 1951 alone. Highway bridges were also
attacked but proved to be more difficult to interdict effectively than
rail bridges. Bypasses were sometimes built at a considerable distance
from the original bridge and were thus not easily sighted; fords were
built and used during much of the year.
Truck traffic was uncommon during the daylight hours and at night
was hard to locate and to attack effectively. The results of night at-
tacks against motor vehicles as well as rolling stock were especially
difficult to assess. Trucks usually traveled in convoys of 15 to 20
vehicles, ordinarily under blackout conditions. The mileage, norm
for trucks per night was about 60 miles. For example, a round trip
from the Manchurian border to the battle zone required about 10
nights' travel.
d. Night Operations
Even before Operation Strangle began, the North Koreans had
started to move virtually all rail and road traffic at night. The B-26
bomber was used extensively as a night intruder to harass trucks and
trains along major enemy supply routes. During Operation Strangle,
1,500 to 2,000 sorties were flown monthly by B-26 bombers, about 90
percent of them at night. The heavier B-29 bombers were used to
attack targets at night.
In the absence of bright moonlight, B-26 attacks achieved only
limited success, and numerous experiments were conducted with flares
to light the targets. Infrared detection systems`were used on a limited
scale to locate targets such as locomotives, tanks, vehicles, and indus-
trial locations. The results of these innovations were limited, however.
In 1952, as Operation Strangle disrupted railroad lines, the North
Koreans and Chinese made more intensive use of trucks to transport
supplies to the front. In the fall and winter months, sightings of
vehicles declined, and the B-26 night attacks were shifted to rail cut-
ting and to harassing North Korean night repair activities.
The major lessons from US night-intruder operations during the
Korean War were the following: (1) aircraft, especially the B-26 that
had been designed for day operations, had only limited success at night
in detecting, identifying, and attacking moving targets; (2) air crews
required careful selection and special training for night operations;
and (3) a strong need existed for a family of "denial" weapons that
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would successfully interdict rail lines and highways for periods that
would eliminate the need for essentially inefficient night operations.
Night operations were hampered throughout by the inadequacy of
night photography to provide adequate assessment of bomb damage.
e. The Wa: dong Chokepoirit
The Korean War offers an excellent example of the difficulty of suc-
cessfully interdicting a transportation chokepoint by large-scale aerial
bombing. In the winter of 1952, while Operation Saturate was getting
under way, target specialists located what appeared to be a vital choke-
point near the village of Wa-dong in central Korea about 20 miles
north of the 39th, parallel. Here a major east-west railroad passed
over a highway from Wonsan on the east coast to the capital at.
P'yongyang. About 100 yards further to the west the railroad entered
a short tunnel. The railroad and highway did not follow identical
alignments across North Korea but came together only at Wa-dong.
Adjacent hills rising to about 300 feet above the valley floor would
have made Wa-dong stand out as an ideal chokepoint to even the
most unimaginative target analyst. The North Koreans had used both
the lateral highway and the railroad to shuttle supplies between the
east and west coastal railroads, thus substantially increasing the flex-
ibility of the badly damaged rail system. The objective of the attacks
was to block all rail and vehicle movement in the area. Due to the
area's rough terrain, bypassing the chokepoint would have proved
very costly.
For 44 days, from 26 January to 11 March 1952, 77 B-29 and 126
B-26 sorties saturated the target of about 18 acres with 3,928 500-
pound general-purpose bombs, one bomb for every 22 square yards of
target. Bomb assessment reports for 24 days of the 44-day attack
period showed the following results:
Railroad
Serviceable ..................................................... 10 days
Unserviceable .................................................. 8 days
Status unknown ................................................ 6 days
Total ........................................................ 24 days
Highway
Serviceable ..................................................... 15 days
Unnserviceable ................................................. 4 days
Status unknown ................................................. 5 days
Total ....................................................... 24 days
Bomb assessment reports also revealed that the total effort had
resulted in only 18 actual rail cuts and 15 highway cuts. The effort
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at best resulted in the railroad being interdicted for 8 days and the
highway for 4 days. Except for temporary disruptions the North
Koreans had suffered very little damage. The bombs had done little
more than churn up the countryside; landslides that had been hoped
for did not occur.
Evaluations made of the Wa-dong experience during the Korean
War led to the conclusion that it is a fallacy to assume that there is an
"area target" for traffic interdiction, and the Far East Air Forces recom-
mended that airpower be concentrated on pinpoint bombing against
definite targets in preference to area bombing in any future interdiction
attacks.
1. Early Bombing
North Korea's modern industry, which was developed by the
Japanese, was considerably greater in total capacity and range of out-
put in 1950 than North Vietnam's industry in 1965. During the initial
months of the Korean War the B-29's available in the war theater
were engaged in close tactical support of the hard-pressed US and
South Korean forces. Attacks on industrial targets in North Korea
were not feasible until mid-July 1950. In the next three months the
FEAF Bomber Command dropped 10,400 tons of bombs, with ex-
cellent results, on the major targets listed in Table 3. Of 20 strategic
targets designated by the JCS, 18 had been destroyed or severely
damaged by the late September.
In September 1950, plans were under way to destroy the modern
complex of hydroelectric generating plants that had been built by the
Japanese. On 26 September, 17 B-29's attacked and inflicted minor
damage on the Pujon Hydroelectric Plant, which had an installed
capacity of 128,000 kilowatts. The same day, however, the JCS sus-
pended attacks on strategic targets.
By late September the Commander of FEAF was able to claim,
"Practically all of the major military targets strategically important
to the enemy forces and to their war potential have now been neu-
tralized." In a few weeks, North Korea's modern industry had been
destroyed. Although such destruction obviously inflicted "punish-
ment" on North Korea's leadership, the military effect of the strategic
bombing was of little consequence. Military equipment and ammuni-
tion continued to flow into North Korea from China and the USSR.
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Strategic Targets Attacked in North Korea
1950
Bomb
Tonnage
Percent
of Target
Destroyed
or
Damaged
Wonsan ............... Dock area.........................
Locomotive shops .................. .
Railroad yards ......................
Chosen oil refinery ...................
Hungnam .............. Bogun Chemical Pla.nt...............
Chosen Nitrogen Fertilizer Company. .
Chosen Nitrogen Explosives Company..
P'yongyang............ Arsenal ............................
Kan-Ni ............................
Shunting yards. .....................
Railway shops and yards .............
Chongjin .............. Harbor and submarine base........... .
Mitsubishi ..........................
Iron work .........................
Raiilroad yards and shops .............
Raskin ................ Oil storage .........................
Dock area ..........................
Railroad shops and ;yards .............
Chinnampo ............ Marshaling yards ....................
Port and submarine base .............
Mining and smelter, ..................
Chosen Riken Metals Cc .............
Changjingang Reservoir. Pujon Hydroelectric Plant No. 1..... .
Hamhung .............. Railway shops and yards .............
Haeju ................. Chosen Nitrogen Explosives Company.
Railway shops and yards .............
Kyomipo .............. Iron works .........................
Marshaling yard ....................
Kowon ................ Railway shops and yards.............
Songjin ................ Steel works .........................
Ma.gnesite Chemical Industry .........
Railway shops and yards .............
Yangdok .............. Railway shops and yards............
Namgungni.......... .. Storage area .........................
Munpyongni ........... Rising Sun Oil Storage ...............
Chongju ............... Railway shops and yards .............
Kilchu ................ Marshaling yards.. . .................
Sunchon ............... Chemical industry and marshaling
yard.
Sariwon ............... Marshaling yard ....................
244 50
372 70
477 70
327 95
695 70
563 85
500 85
99 70
500 15
356 30
584 70
249 5
132 30
203 20
1,063 55
49 Negl.
218 Negl.
110 Negl.
121 80
5 Negl.
248 35
284 70
39 10
547 70
568 10
104 70
252 40
23 Negl.
102 10
326 90
183 30
280 60
75 85
58 80
2
170 10
99 50
138 30
81 50
Total ..................................................... 10,446
No bomb damage assessment.
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2. Later Strategic Bombing Efforts
a. Hydroelectric Power
It was not until June 1952 that the hydroelectric installations pre-
viously regarded as "politically sensitive" targets were again considered
as legitimate targets. Over a 3-day period in June 1952, 730 fighter-
bomber sorties by the Fifth Air Force, supported by sorties from a
Navy Task Force, were flown against the power complexes, including
the Sui-ho Generating Plant on the Yalu River. Poststrike evaluation
of the bombing attack indicated that 90 percent of North Korea's elec-
tric power capacity had been knocked out. For more than two weeks
there was almost a complete blackout in North Korea until small
thermal plants and undamaged hydroelectric plants restored a small
portion of North Korea's pre-attack capacity. Although the small,
dispersed "war-industries" in North Korea obviously suffered from the
loss of electric power, the extent of the damage to industry in Man-
churia, which received much of its electric power from North Korea,
was difficult to assess.
Attacks against the hydroelectric installations came much too late
in the Korean War to have much impact on the outcome or to do serious
damage to North Korea's war effort. The attacks were designed
primarily to exert continued air pressure on the North Koreans and
Chinese to accept UN truce proposals.
b. Irrigation Dams
In the spring of 1953, only slow progress was being made at the
Panmunjom truce talks. Air Force targets specialists seeking addi-
tional means of increasing air pressure against the Communists recog-
nized the importance of the irrigation dams to Korean rice production.
There followed a large-scale and highly successful attack against a
2,300-foot earth and stone dam about 20 miles north of P'yongyang.
Along with severe damage to a major rail line, the floodwaters also
damaged 5 square miles of prime rice crops.
Other Korean dams were attacked by US fighter-bombers and B-29's,
ostensibly to interdict transportation lines. These later attacks were
less successful because the North Koreans, as in other circumstances,
improvised countermeasures. For example, by rapidly lowering the
water level the North Koreans made it much more difficult to destroy
or seriously damage the dams.
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1. Introduction
The 27,900 strike sorties flown and the 34,300 tons of bombs, napalm,
and rockets expended under the Rolling Thunder program from Feb-
ruary through December 1965 are less than one-third the 81,600 sorties
flown and the 104,000 tons of bombs dropped by the Air Force during
the interdiction and armed reconnaissance sorties in the 11 months of
Operation Strangle. In addition, during the Korean War Navy and
Marine aircraft operating from carriers probably also dropped about
one-third as much tonnage as was dropped by the Air Force on inter-
diction targets.
Even allowing for exaggerated[ damage claims, it is clear that there
were far more lucrative targets in North Korea than are being located
and destroyed presently in North Vietnam. Destruction claimed in
the 11 months of Operation Strangle in Korea compared with that
claimed for Rolling Thunder in Vietnam through December 1965 is
shown in the following tabulation:
OPERATION STRANGLE
ROLLING THUNDER
Locomotives ............................
272
6
Freight cars ............................
3,638
227
Vehicles ...............................
33,210
483
Bridges ................................
223
161
Buildings ...............................
9,109
1,837
........................
Barges and boats
22a
`'
480
The greater destruction achieved in Korea compared with North
Vietnam is not solely a function of the number of sorties and the ton-
nage of bombs dropped. The Rolling Thunder program has had to
operate under policies which sharply limit both the areas in which it
can operate and the targets it can attack. North Korea's railroads and
highways had to supply almost 1 million troops, 600,000 of whom
were at the front. North Korea had almost 2,300 miles of rail lines
and 10,000 miles of highways, compared with North Vietnam's meager
485 miles of rail lines and 5,800 miles of highways. North Korea had
a much larger park of 'both rolling stock and trucks. In addition, al-
though the population of North Vietnam substantially exceeds North
Korea's, there was more modern and semimodern industry in North
Korea than is found in 'North Vietnam.
2. Failure of the Interdiction Campaign
At the time Operation Strangle was under way, it was estimated
that each Chinese division required 50 tons of supplies per day.* With
* About 48 percent food; 2'2 percent clothing, weapons, and equipage; 10 percent POL;
and 20 percent ammunition.
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60 divisions at the front, approximately 3,000 tons of supplies had to
be moved from Manchuria to the battlefront each day.
Peacetime capacity of the double-tracked line in western Korea
from Sinuiju to P'yongyang was estimated to have a capacity of from
6,000 to 9,000 tons per day. After maximum interdiction efforts, it
was conservatively estimated that only 500 to 1,500 tons per day were
getting through to the battle zone. The capacity of the east coast rail
line, 5,000 tons per day in peacetime, was reduced to less than 500
tons per day. Thus railroads were still able to transport about one-half
of the daily requirements. In addition, the North Koreans and Chinese
also relied heavily on trucks and on peasants carrying supplies strapped
to A-frames and even bicycles for .moving supplies to the front. A
staff study completed in April 1952 by two Air Force officers concluded
that after seven months of maximum US effort the Communists still
were more than meeting minimum supply requirements. The study
concluded that the accepted figure for the enemy's minimum supply
requirements was 2,700 tons per day under existing conditions but
that more than this amount was being received. The staff study also
stated that over and above daily requirements the enemy had been
able to stockpile approximately 100,000 tons, or a 37-day supply, dur-
ing the seven months of the rail interdiction program. This capability
was, however, not sufficient to permit the North Koreans and Chinese
to mount sustained offensive operations.
Another logistics study from the Korean War illustrates how difficult
it is to prevent what was called "seeping resupply." During three
months in the winter of 1951-52 the Chinese and North Koreans were
firing 15,000 mortar shells per month, or 500 shells a day. Each shell
weighed 10 pounds; thus it was possible for a peasant to carry five of
them on an A-frame. One hundred peasants arriving at the front from
supply depots in the rear could supply all the enemy's daily needs for
mortar ammunition. One truck a -day could replenish the supply
depots.
Operation Strangle clearly did great damage to the transport system
of North Korea and conceivably prevented Communist China from
mounting additional large-scale offensives in Korea. At the same time,
it is also clear that the Chinese and North Korean troops received suf-
ficient logistic support to contain the offensive pressures exerted by
the Eighth Army. In short, the defensive capabilities of the Chinese
and North Koreans showed no sign of collapsing as a result of the inter-
diction campaign, and indeed the enemy was able to mount sharp
battalion-size attacks on occasion.
SECRET 31
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The air interdiction campaign failed to deny Communist forces the
supplies they needed to contain the US Army because the North Ko-
reans and Chinese were able to take effective countermeasures. One
major lesson that emerged from the Korean War was that US planners
underestimated the effectiveness of the enemy countermeasures. The
North Koreans and Chinese showed increasing rapidity in rebuilding
damaged rail and road bridges and other key installations. Choke-
points, often given exaggerated importance, were frequently bypassed
without undue enemy effort. Darkness shrouded most of the enemy's
movements from effective attack. A major lesson of the Korean War
was the clearly demonstrated need. for the development of a family
of weapons that could. successfully interdict night railroad and high-
way traffic.
3. Air Pressure Tactics and Psychological 'Warfare
It is difficult to judge the overall effect of US interdiction and
strategic bombing on the will of the political[ leadership and the morale
of the civilian population of North Korea. There are numerous ex-
amples, however, of the North ]Koreans and Chinese responding with
effective countermeasures to each new phase of air operations against
North Korea. The North Koreans were able to devise effective means
to counteract the program of massive rail interdiction. The North
Korean response to the bombing; of irrigation dams also illustrates the
tenacity and cleverness with which the Communists met new phases
of US air operations.
Claims by some historians that air operations were almost solely
responsible for the North Koreans and Chinese initially coming to the
conference table and finally signing a truce agreement cannot be sub-
stantiated.* The Chinese and North Koreans came to the conference
table mainly because their total losses accruing from the war had
become greater than their total gains, all military, political, and eco-
nomic factors considered, including losses from air attacks. US air-
power played an important role in. convincing the Communists to come
to terms, but the evidence does not support the view that airstrikes
were the decisive factor.
Because of a host of factors, including the unique nature of UN
"police action" in Korea and the uncertain position of US officials about
the advantages and disadvantages of psychological air warfare, the
^ One Air Force historian, for example, in discussing FEAF operations in Korea in mid-1952,
wrote, "the destructive force of FEAF's airpower has broken the stalemate."
32 SECRET
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psychological warfare phase of US operations in North Korea was
little understood and only intermittently applied.
4. Lessons for Vietnam
The lessons from the Korean War indicate that it will prove difficult
to cut off supplies flowing from North Vietnam to South Vietnam. The
total daily tonnages needed by the Viet Cong and North Vietnamese
regulars engaged in South Vietnam are far less per man than was the
case in Korea, largely because most food and clothing supplies are
obtained locally in the South. Relatively small numbers of trucks,
carts, and human bearers can maintain more than the enemy's mini-
mum requirements unless the Vietnamese war is sharply escalated.
Furthermore, the experiences of the Korean War suggest that as long
as they continue to receive extensive support from China and the USSR
the North Vietnamese are likely to show an increasing capability to
improvise countermeasures to circumvent a continuing US air inter-
diction. The Korean War suggests also that diminishing returns can
be expected from continuing air interdiction. At the same time, the
increasing effectiveness of conventional antiaircraft weapons and air
defense missiles could raise the cost of continuing the campaign. The
rebuilding of bridges, the building of bypasses, and the other counter-
measures in evidence in North Vietnam in no way suggest a less 'de-
termined enemy than was encountered in Korea. The primitiveness
of North Vietnam-the lack of potentially decisive military and indus
trial targets-will make it difficult if not impossible for airpower alone
to extract a prohibitive price for North Vietnamese intransigence.
Only the application of large numbers of new interdiction weapons
which are more effective than those that were available in the Korean
War would be likely to tip the scales in favor of successful, long-term
interdiction.
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Munitions
Production
100
Effect of Allied Bombing on German Munitions Production
Munitions Production
(Average month 1941=100)
Bombs Dropped
1942 1943 1944 1945
E-1 Effect of Allied Bombing on German Munitions Production
Munitions
Production
Effect of Allied Bombing on Japanese Munitions Production
and Maritime Shipping
~--~~ Munitions Production
(Average month 1941 = 100) -- - _ ..a ._._ . ._.
Bombs Dropped
Seaborne Traffic by Civilian
Merchant Marine
E-2 Effect of Allied Bombing on Japanese Munitions Production and Maritime Shipping
Bombs
(Thousand tons per quarter)
Bombs Seaborne Traffic
(Thousand tons (Thousand metric
per quarter) tons per quarter)
1941 1942 1943 1944 1945, 1946
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Indexes of Bombs Expended and 'Value of Destruction in the Korean War
During Operation Strangle
August 1951-June 1952
Index of Bombs Expended (Tons)
Index of Damage per Ton of Bombs
Index of Value of Destruction
Oct. Nov. Dec. T, Jan. Feb.
Mar. Apr.
1952
E-3 Indexes of Bombs Expended and Value of ]Destruction in the Korean War
During Operation Strangle
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Mr. whitin~d',s office in State (Director, 0/
Research and Analysis for called to say that
they consider hR 66-B, ]I i storical Notes on the U."c
of Air Power as a W(,o.pon. oL' I nterdiction, an excel
Lent report and W)u.l.d like to make wider dissernina
tion of it. They have rcc:uestcd 12 more copies
and St/P/C is _L' i..i .L:i n;; the order. This report was
sent to Div I-TuChc1, i-NR, over your signature.
i' 7udy
g1_)UMa:y 66
(DATE)
I'ORM NO.
I AUG 54
HCPLACFS FORM 10-101
W11 I CII MAY UL USED.
STATINTL
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STATINTL
TRANSMITT -L SLIP
DATE
23 May 1966
TO:
Ch/D/T
ROOM NO.
BUILDING
3 G 39
Hq
REMARKS:
FYI --
copy placed in ORR
Commendation
File.
Trudy
FROM:
DD
/ORR
BY-3
ROOM NO.
BUILDING
EXTENSION
1 FFEB ORM 55 24 I REPLACES FORM 36--8
WHICH MAY BE USED.
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