Intelligence Operations of OSS Detachment 101


22 SEPT 93

Aspects of a classical scouting and resistance-leading unit behind Japanese lines in Burma, from the viewpoint of its commander. 



W. R. Peers

For Detachment 101 intelligence was an all-pervasive mission. The Detachment did plan and carry out espionage operations specifically to collect both strategic and tactical information, but intelligence was also a by-product of all its other operations, including guerrilla actions, sabotage, and psychological measures. Its intelligence activities were therefore augmented rather than decreased when large-scale guerrilla operations were initiated in the spring of 1944.


Early Operations

The history of Detachment 101 began in the spring of 1942, when a small group of officers and men was assembled in Washington under the Office of the Coordinator of Information. Captain (later Colonel) Carl Eifler was the first commander. After a short period of training and equipping, the unit shipped overseas to the China-Burma-India Theater. In the summer of 1942 it received its first directive from General Stilwell, short and to the point: "Establish a base camp in northeast India and from there plan and conduct operations against the roads and railroad leading into Myitkyina in order to deny the Japanese the use of the Myitkyina airfield. Establish liaison with the British authorities to effect coordination with their operations."

The remainder of the year was spent in locating and developing a base camp in Assam Province of northeast India and recruiting and training agent personnel for subsequent operations. An office was established in Calcutta to receive supplies from headquarters in the United States and to procurebulk goods from the Army Service of Supply. At that time there was available no small, portable military or commercial radio capable of transmitting from northern Burma to Assam, a distance of 200 to 500 miles. Accordingly it was necessary for the unit to design and construct its own radio set. The result was crude, but it worked well. It became the model from which the SSTR series of sets was built by OSS, which by now had succeeded to the intelligence and paramilitary function of COI.

In 1943 exploratory field operations were carried out in Burma on a trial-and-error basis. Some of them were failures; but they taught us many lessons as to what could be done and, even more important, what should not be done. By the end of the year six base camps had been established behind the lines in northern Burma, three east of the Irrawaddy River and three to the west. Each of these had recruited an trained a small group of indigenous Kachin personnel for local protection and to perform limited operations, principally simple sabotage and small ambushes. Each also trained a few native personnel as low-level intelligence agents, who reported their information by means of runners or via the bamboo grapevine. From the field bases this information was forwarded to the base camp in India by radio. By the end of the year it was possible to assemble a fairly comprehensive picture of Japanese strengths and dispositions in northern Burma.

The field bases also selected native recruits for more intensive intelligence training. These were flown by light aircraft or infiltrated through the Japanese lines to the airfield at Fort Hertz in the northern tip of Burma and thence flown to the base camp in India. Their training, of three to five months duration, followed the normal curriculum for intelligence agents. The Kachins were particularly adept at CW radio communications; by the end of the course most of them were able to operate at 25 to 45 words per minute. When their training was completed, some of them were returned to their field bases to expand local information procurement and others were parachuted into Burma for independent operations.


The Myitkyina Campaign

With the initiation of orthodox military operations in the winter of 1943-44 by the Chinese ground forces, later augmented by Merrill's Marauders, General Stilwell directed the Detachment to expand its guerrilla force to a strength of approximately 3,000 in order to assist in the drive down the Hukawng Valley and the eventual attack on Myitkyina, and also to extend its intelligence operations south of Myitkyina at least to the area of Bhamo and Katha. He made available the arms, ammunition, personnel, and airlift necessary to fulfill this directive. He also stated that should the Detachment be successful in providing this clandestine support to the combat forces, approval would be forthcoming to expand its guerrilla forces to a strength of 10,000, with a commensurate increase in intelligence and other operations.

That the Detachment was indeed successful in this assignment can be illustrated by several incidents from the Hukawng-Myitkyina campaign. The final drive on Myitkyina was made in May 1944 by the Galahad Force (Merrill's Marauders and two Chinese regiments) across the Kumon Range and thence south through Arang to the Myitkyina airfield. Detachment 101 assisted this movement by providing two coumpanies of Kachin guerrillas to reconnoiter and screen the front and flanks. When the Galahad forces reached Arang they picked up additional guides and scouts from a Detachment field base located there. One of the scouts, who had been bitten by a poisonous snake and was so weak that he had to ride horseback, nevertheless led the Galahad Force to the airfield over some old unused trails, completely surprising the Japanese. The airstrip was thus occupied with but little resistance. The part played by the Detachment in this operation points up the interrelationship between its intelligence and other activities.

A day or so before the Galahad Force seized the airfield, Detachment 101 had some of its agent personnel in and out of Myitkyina town. They estimated the Japanese strength there at that time to be only approximately 300, and this information was given to the Northern Combat Area Command and the Galahad Force. After the airstrip was seized, two Chinese units were therefore assigned to secure the town. It was to be a double envelopment, one Chinese unit moving north along the Irrawaddy River and the other attacking from the west. All went well until the two converged on the railway station in the center of town at about dusk. It has been reported that Japanese snipers between them started picking them off. Whatever the reason, they soon became heavily engaged with each other and inflicted such severe mutual casualties that they had to be withdrawn. The attempt at an early seizure of the town thus came to nought.

It was two days before the forces were reorganized and made another assault on the town, and when they did they encountered a hornets' nest. In the interim the Japanese had reinforced the town from every direction. They came by road and railroad from Mogaung to the west, from the supply installations to the north along the Irrawaddy, from Maingna and Seniku across the river from the town, and from elsewhere. Within two days, it was estimated, Japanese strength in the town had been augmented to over 1,500, by the end of a week it exceeded 3,000, and it still continued to grow.

This build-up was so rapid as to create for a while the feeling in some quarters that our original strength estimates must have been wrong. But Detachment intelligence agents and guerrilla patrols placed along all the access roads and trails leading into the city confirmed by observation the frantic effort of the Japanese to reinforce the garrison. And subsequently the interrogation of Japanese POW's by NCAC and Galahad intelligence staffs verified as proximately accurate the 300 figure which had been provided by the Detachment. The only discrepancy was in the other direction: an original strength figure of 275 for the Myitkyina garrison was obtained through the interrogations.

The battle for Myitkyina town continued beyond June and into the monsoon. Meanwhile Detachment 101 had expanded its activities to the south as directed by General Stilwell and was providing intelligence and operational support to the combat forces. By the time Myitkyina fell to the allied forces in August 1944, the Detachment had organized its guerrilla forces across an area generally 100 miles farther south and was well on its way toward its ultimate strength of 10,000. Intelligence operations were also increased, and espionage groups were deployed along Japanese lines of communication as far south as Toungoo, approximately 400 miles away.


Mandalay and Beyond

In the fall of 1944 the allied forces in northern Burma opened their drive from Myitkyina toward central Burma. Detachment 101 moved its guerrilla operating area to a line generally through Lashio to Mandalay and thence to the Chindwin River and the India border. At that time it reached its greatest strength and highest stage of development. In the area of Lashio there were seven separate battalions, each capable of independent operations. North of Mandalay there were approximately 2,500 guerrillas, organized into units of varying size, depending upon the local situation. To the west, between the railway corridor and the British 14th Army in the Imphal area near the India-Burma border, lay a stretch of over 250 miles in which no allied combat forces were operating. Through this gap ran a series of parallel corridors, excellent natural approaches for the enemy to the Ledo Road being constructed behind the allied combat forces. General Sultan, who had succeeded General Stilwell as Commanding General NCAC, directed Detachment 101 to utilize its guerrilla and intelligence resources to block these several approaches Guerrilla forces were accordingly deployed in each of them, and with information supplied through intelligence activities were able -- although not without some severe fighting--to fend off several Japanese probes through the area.

Intelligence operations during this phase of the campaign were widely developed and reached their greatest degree of reliability. There were over 100 operations involving in excess of 350 agent personnel. Through these and the collection of information by the guerrilla forces, Detachment 101 was able to stay abreast of the changing organization, deployments, and strengths of the Japanese forces. In fact, its intelligence officers probably knew at least as much about the Japanese tactical organization and capabilities as the Japanese themselves did.

When Lashio and Mandalay were captured by allied forces, the Detachment was directed to withdraw its forces from the field and inactivate. Soon, however, the combat situation in southern China became extremely critical, and it was necessary to withdraw all Chinese and American combat forces from northern and central Burma to try to stem the Japanese drive there. General Sultan therefore directed the Detachment to reconstitute whatever force was necessary to conduct a mopping-up operation in the southern Shan States and seize the Taunggyi-Kengtung road, the Japanese escape route to Thailand. Most of our intelligence operations had been retained fortunately, so there was a sound basis for embarking on this assignment: with some of the Kachin guerrillas as a nucleus, a force approximately 3,000 strong was organized into four battalions. The Japanese, however, had evidently not been told that this was to be a mopping-up operation; it resulted in some of our bloodiest fighting of the war. In less than three months the Detachment's forces killed over 1,200 Japanese and suffered more than 300 killed in action themselves, far more than in any other period. When the escape route to Thailand had been secured, Detachment 101 was inactivated. This was 12 July 1945.


Requirements and Collection

Intelligence requirements on the Detachment stemmed from a variety of sources. Tactical information was required chiefly by Headquarters NCAC, its subordinate commands, and the 10th Air Force, but requests were also received from the British 14th Army and Headquarters Allied Land Forces Southeast Asia. Information of a strategic type would be requested by higher OSS headquarters, CBI Theater Headquarters, and the allied Strategic Air Command under General Stratemeyer in Calcutta. Detachment 101 itself required information of all varieties for planning and conducting its field operations.

With the NCAC, broad intelligence requirements were normally received from the Commanding General in conference. Specific requests came through the Detachment's liaison officer maintained on his G-2 staff. The same general procedures obtained with the 10th Air Force. On the basis of these requirements, along with all others, an intelligence plan would be drawn up, outlining the information to be obtained, the probable target areas, and the likely sources. If sources were already available in the target area, they could simply be asked for the information through normal communication channels. When sources were not available, it was necessary either to adjust operations to obtain the information or to plan new intelligence operations, for which indigenous personnel would have to be recruited, trained, and infiltrated.

The infiltration of agent personnel into proposed areas of operation was effected by parachute or light aircraft or along land routes. The infiltration procedures were in general similar to those used in other theaters of war; but there was one device we employed that involved a unique use of pigeons. Each agent parachuted behind the lines had attached to him a small bamboo cage just large enough to hold a pigeon by which he could report the condition of the radio that had been dropped along with him. After the agent had landed, cleared the drop zone, and had an opportunity to test his radio, he would release the pigeon, preferably near daylight, with a coded message either indicating that all was well or giving instructions when and where to drop another one. For ranges up to two or three hundred miles the pigeons were highly reliable; beyond 400 miles their dependability decreased rapidly.

The intelligence requirements levied on the Detachment were such that almost anything taking place behind the enemy lines was of interest. Primary emphasis was placed upon military information, such items as the strength, identity, and movement of Japanese units, details on supply installations, airfields, and equipment, and whatever else was required to provide a continuous, composite picture of the enemy situation. Much terrain information was also reported, principally on the condition of roads and railroads, the water level and fordability of streams, and the location of potential airfields and drop zones. Since most of the Detachment's personnel were indigenous to the area and intimately familiar with its physiography, this information was rather easy to assemble and report. Economic, sociological, and political intelligence was also in great demand in higher OSS headquarters in the theater, in such agencies as OWI for psychological warfare operations, and in air units for pilot briefing and survival training. It was also needed by the Detachment itself both for morale operations aimed at psychological subversion and for developing agent cover.

The main sources of information were the numerous intelligence agents trained at the Assam base or in the field. Each major field unit had an intelligence officer, usually an American but in some instances a foreign officer or an indigenous recruit trained for the position, whose principal duties were to interrogate captured enemy soldiers or agents, debrief guerrilla personnel, and direct the activities of the espionage agents assigned to the unit. Intelligence personnel at the forward operational headquarters and at the base camp were also engaged in collecting information, principally through interrogation of prisoners and debriefing of operational personnel returned from the field.


Weather and Air Targets

In conjunction with Air Weather Service of 10th Air Force, the Detachment developed a capability for collecting and reporting weather data. The Weather Service provided the equipment, instruction, and weather codes. These were given to selected agents who were then so dispersed, singly or with other groups, that in the aggregate they provided coverage of all of central and northern Burma. According to the A-2, 10th Air Force, this service was of considerable assistance in developing meteorological forecasts for cargo flights over the "hump" and for tactical air operations in northern Burma.

Of especial interest were some of the procedures used in reporting air targets for the 10th Air Force. In the lower reaches of the Hukawng Valley an intelligence agent worked out some simple but ingenious ways to pinpoint and report Japanese supply installations concealed by dense jungle foliage. One method was to select a landmark such as a trail junction, bridge, or prominent tree which could be identified readily on an air photo or by the pilot of the fighter-bomber aircraft. From the landmark the location of the target was given by polar coordinates (distance along a given azimuth). Another method was to lead the pilot from such a landmark to the target by a series of reference points.

Numerous Japanese installations located by these means were bombed or strafed without the pilot being able to see his target; huge explosions or fires erupting through the trees would indicate a successful attack. The Japanese knew that something was amiss. Since the targets were completely hidden from the air, they deduced that the attacks were being directed from the ground and suspected the Kachins. They accordingly restricted entry to their supply areas and would shoot a Kachin on sight. To protect the Kachins these operations had to be suspended for a time.

In the later phase of the Burma campaign procedures were worked out with the 10th Air Force for immediate air strikes against targets of opportunity. Pilots flying air alert and agents on the ground were given duplicate sets of air photos with a special grid superimposed. To obtain action against a target the agent would send a coded radio message specifying the type of target and its grid location to the Detachment's forward operations headquarters, located in the immediate vicinity of Headquarters NCAC and the 10th Air Force. 10th Air Force would relay this to the pilot in the aircraft, and after a normal elapsed time of 20 to 30 minutes from the origination of the message an air strike would be made on the target.


Transmission Channels

To expedite the flow of intelligence to user agencies the Detachment established comprehensive handling and transmission procedures. All messages from the field came in to the forward operations headquarters, where field operations were coordinated by an operations officer and a staff including members of the morale operations, intelligence, resistance, and other sections. The intelligence personnel on the operations staff screened all incoming information. If it was of an urgent nature, it was given a hasty evaluation and immediately dispatched to the using agency. Other intelligence messages were routed to the intelligence section for review and subsequent transmission to user agencies on a routine basis.

Detachment 101 had liaison groups with each of the major combat commands it supported--NCAC, 10th Air Force, British 14th Army, and ALFSEA. These officers represented the Detachment in all operational matters, an arrangement that served to enhance their stature and give them considerable prestige in their intelligence dealings within the headquarters. Intelligence-wise, they were responsible for accepting information requests from the headquarters and forwarding them to the Detachment, for passing information and intelligence received from the Detachment on to the intelligence staff, and for representing the Detachment in all other intelligence matters. Information was transmitted to NCAC and the 10th Air Force by teletype and could be moved most rapidly. The communication link with 14th Army and ALFSEA was radio, which required additional time for coding and transmission; the elapsed time, however, was sufficiently small that it could be measured in terms of minutes.

Field liaison groups were also maintained with the Chinese 1st and 6th Armies, the British 36th Division, and the Mars Task Force, which had succeeded Merrill's Marauders. These liaison groups were small, normally consisting of one officer (generally one with considerable field experience) and a radio operator. They performed intelligence functions comparable to those of the higher headquarters liaison groups.

The intelligence transmitted via radio and teletype was summarized and supplemented in the Detachment's weekly and monthly situation reports, distributed through ordinary military messenger service. These were given fairly wide distribution in the theater, going to approximately 100 agencies.


Reliability and Security

Detachment personnel concerned with the evaluation of information arrived at some unusual conclusions. They found, for example, that information reported by the Kachins was generally highly accurate, but that their reports of enemy strength were almost invariably about three times the actual figures. Strength reporting was then stressed in the training program to the extent that the pendulum swung the other way, and the strengths given in Kachin agent reports were so underestimated that they had to be increased by a factor of three. It was not until the winter of 1944-45 that it was possible to obtain reliable strength figures from Kachin personnel. Other ethnic groups were found to have comparable traits, more or less uniform within each group. The evaluators developed correction factors for the Shans, Chins, Burmese, Padaungs, and even the remnants which had remained behind in Burma from the original Chinese Expeditionary Force. All of these groups overestimated strengths, but the Chinese grossly exaggerated them. Their strength figures had to be reduced approximately ten times, and this practice remained constant to the end of the campaign.

The Detachment's counterintelligence operations were purely defensive, designed to protect it and its field operations from infiltration by enemy agents. The number of counterintelligence personnel assigned was consistently small, 3 to 5. They arranged for the physical security of base installations and for the indoctrination of U.S. and indigenous personnel. The indoctrination was concerned principally with the methods used by Japanese agents to penetrate and mislead allied clandestine operations and with means for isolating such agents. Counterintelligence functions in the field were the responsibility of the Area Commander or Group Leader in charge of a unit. As a general rule the commander relied mainly on his intelligence officer to ferret out enemy agents, uncover double agents, and of course determine what should be done with them. The Detachment attempted to make all personnel security and counterintelligence-conscious for their own benefit and to avoid attracting undue attention to the clandestine activity. As a result, the security of the Detachment and its operations, despite some minor infractions, was very good. Not a single agent or operation was known to have been eliminated through enemy intelligence penetration.



Detachment 101's two principal intelligence consumers made attempts to weigh its intelligence contribution to the northern Burma campaign. G-2, NCAC, estimated that it provided between 80% and 90% of all of the combat intelligence utilized by that headquarters. The 10th Air Force reported that it furnished up to 70% of its usable information and designated between 90% and 95% of its air targets. In addition, the Detachment was one of the principal sources of bomb damage assessment information for the 10th Air Force and for SAC. No attempts were made to measure the intelligence contributed to other headquarters, but letters of appreciation showed that it was welcome and considerable. This intelligence was also an indispensable ingredient in the development of the Detachment's own resistance and other clandestine operations.

Units comparable to Detachment 101 collected information behind the lines in France, Italy, the Philippines, China, and other areas. In the aggregate they represented an immense intelligence capability of a type for which, if there should be another war, there would in all probability be a strong requirement. Each of these operations, however, experienced growing pains, and there was a lag time of from one to two years before they were able to produce tangible results. It would be highly desirable, therefore, that the personnel who may be used in such operations in the future should be so oriented, trained, and organized that this critical lag could be minimized. How this is to be accomplished appears as a pressing and continuous problem for the intelligence community.

Historical Document
Posted: May 08, 2007 07:30 AM
Last Updated: Jul 01, 2008 10:16 AM