Engineering the Berlin
ago, the CIA embarked on a project to intercept Soviet and East German messages
transmitted via underground cable. Intelligence was collected to determine the
best place to hit the target, and then concrete planning for a new collection
site was begun.
The tunnel was 1,476 feet in length and consumed 125 tons of steel liner plate and 1,000 cubic yards of grout . . . This was not a small operation!
Early in 1951
when I was working in the Engineering Division of the Office of Communications,
I received a message from some people in the office of the Deputy Director of
Plans—specifically the chief of Foreign Intelligence/Staff D (FI/D), and a
member of his team—requesting a meeting. 
The meeting was short. The only question they asked was whether a tunnel could
be dug in secret. My reply was that one could dig a tunnel anywhere, but to
build one in secret would depend on its size, take more time, and cost more
money. After the meeting, I was transferred to FI/D. Thus began planning for
the construction of the Berlin Tunnel.
building the tunnel in August 1954 and completed it in February 1955. It was
1,476 feet in length; 3,100 tons of soil were removed; 125 tons of steel liner
plate and 1,000 cubic yards of grout were consumed. This was not a small
swirled around the net intelligence value of the operation.  But the completion of this demanding
project—accomplished in secret and under exacting conditions—is a tribute to
the resourcefulness and expertise of an outstanding team of professionals.
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Learning as We Went
Prior to this
project, my tunnel experience was limited to several night-shift visits to the
Brooklyn-Battery Tunnel as a student civil engineer. Constructed in 1948 and
somewhat unique, the tunnel extended from Battery Park in lower Manhattan to
South Brooklyn. It was designed for two 18-foot bores, which were mostly
blasted and drilled in solid rock. The East River crossing presented a problem,
however. At the confluence of the East River and the Hudson River, there was a
deep submarine canyon, a leftover from the extensive land erosion caused by the
violent runoff of melt waters from the retreating Continental Glacier. The
canyon was filled with the muck and detritus of eons of erosion. This fact
required that a pressurized shield, solely for the prevention of blowouts on
the East River crossing, had to be moved the entire length of the tunnel. The
concept of such a shield surfaced in design discussions for the Berlin Tunnel
project. The Brooklyn-Battery Tunnel demonstrated the magnitude of the job of
marshaling the experienced personnel, materials, and equipment for the huge
task of constructing a tunnel and disposing of the excavated soil. Work on the
18-foot bore tunnel could not have been done in silence. These matters were a
warning, because silence would be a top priority in constructing the Berlin
Tunnel in secret.
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Berlin project received a green light, design specifications had to be
determined; men and materials assembled; and questions of site selection,
training, and transportation answered. The big question that loomed was how to
dispose of the tons of soil that would be excavated! Rough calculations showed that the amount of
soil expected to be brought out from the tunnel and vertical shaft would fill
to the brim more than 20 living rooms in an average American home! Security and silence dictated that not one
cubic foot of soil be removed from the site. A warehouse, with a basement for
the storage of the excavated soil and a first floor reserved for recorders and
signal equipment, was the solution.
Soil from the tunnel would fill more than 20 living rooms in an average American home!
My task began
with an inspection of existing tunnels in the Washington, DC, area, which
included utility bores, pedestrian walkways, storm drains, and railroad
maintenance tunnels. From this research, I concluded that our tunnel should be
6 feet in diameter with a structure of steel-flanged corrugated liner
plates—the 6-foot diameter would provide a comfortable working room at the
tunnel face. Next came research at the Library of Congress to check the
available literature dealing with earth pressures on tunnels. I already had two
textbooks and found three relevant papers published by the American Society of
Civil Engineers. Together, these provided the procedures I needed to start the
mathematical analysis of the tunnel structure.
In the spring
of 1953, I flew to Frankfurt, Germany, to meet with a senior case officer at
the CIA station. The officer told me that the tunnel site had not yet been
selected. He also advised me that Lt. Col. Leslie M. Gross had been selected as
the tunnel’s resident engineer. He expressed regret that I had not been
selected. I told him not to worry. 
subject we discussed was a meeting with the British in London. We would attend
this meeting with Bill Harvey, chief of our Berlin base. At the beginning of
the meeting, I started to discuss some notes I had on the unfinished
mathematical analysis of the tunnel structure. Clearly the attendees were not
interested in mathematics. The discussion turned to the matter of the form of
the tunnel design. The British proposed using heavy concrete blocks, which were
common in the London Underground. I countered with the idea of using steel
liner plates, which would be lighter and easier to use in the tunnel and at the
tunnel face. This proposal was accepted.
subject was a question of using a shield. I did not offer an opinion because it
was a topic that I felt should be discussed with Les Gross. Bill Harvey got the
impression that I did not know the difference between a shield and a
coat-of-arms. When we returned to Frankfurt, it was suggested that I make a
drawing of a shield. Normally, a shield—such as the one used on the
Brooklyn-Battery Tunnel—would not be used in a tunnel as small as 6 feet. Other
methods, such as poling, would be used to prevent a collapse of the tunnel
roof. However, I drew an engineering plan for a 6-foot shield, and Bill Harvey
later used the drawing in his request for final approval of the tunnel. 
The ‘circuit method’ of computing earth pressures on tunnels required solving six simultaneous equations.
I had my first
meeting with headquarters. A short conference resulted in an agreement that a
shield should be used. A shield would have the added advantage of keeping the
alignment of the tunnel on course. We selected a prime contractor for the liner
plates and shield, negotiated a classified contract, and work commenced.
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Assembling Men and Materials
Working out of
an office in one of the World War II temporary buildings along the Reflecting
Pool near the Lincoln Memorial, Les started the process of recruiting his team.
He selected Corps of Engineers officers and non-commissioned officers. He also
began to look into a site out West where the liner plates and shield could be
assembled for training for the up-coming real thing.
Les left the
structural analysis to me. Ordinarily, earth pressure on a tunnel is figured at
four points: the overhead, both sides, and the invert. This technique did not
seem adequate. I spent nearly a week at the Library of Congress searching for a
better way of analyzing earth pressures. I found two technical papers that
offered a better approach. The papers discussed the “circuit method” of
computing earth pressures on tunnels. It was a sort of circumferential
calculus. The downside was that the circuit method of calculation required solving
six simultaneous equations! Perhaps this
sophisticated method was a bit of overkill; however, the design assumptions
called for precise planning. The tunnel not only needed to be able to withstand
a dead load of 10 or more feet of soil overburden, but also had to bear a
potential surcharge load—to wit, Soviet or East German 60-ton tanks riding down
Schoenefelder Chausee or maneuvering around the open field above the tunnel.
narrowed the search for a site to test the installation of the shield and liner
plates to New Mexico, I flew back to London for a meeting with Bill Harvey. We
traveled with one of Bill’s British colleagues to a location to view the
operation of the vertical shield needed to gain access to the Soviet
communications cables. The vertical shield was demonstrated by the British
sappers who would operate it at the site. This was a process that required
extreme patience and skill. During the motor trip, I suggested that as a cover
for the tunnel site, we should build one or two communications stations that
would exchange false traffic. This idea was met by icy stares.
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Drawing on the
clandestine sources of the Berlin base, Bill Harvey decided to locate the
operation in a rural area of the American Sector southwest of Berlin known as
Altglienecke. The target cables—two estimated to be in good shape, and a third,
in poor shape—ran in a ditch on the west side of Schoenefelder Chausee in the
Soviet Sector. The aiming point for the tunnel was about 300 yards north of a
usually kept on line and grade by surveys conducted in the tunnel and on the
ground above it by transits and calibrated steel tapes. A surface survey,
however, was obviously inappropriate for a secret tunnel. Having no lasers, we
had to use other methods.
Drawing on the
best technical resources of the time, several photographic over-flights were
ordered. One flight used glass plates for maximum accuracy. The glass plates
were sent to the Agency’s fledgling air photoanalysis unit. They conducted
air-photogrammetry studies to determine distance and elevation. The engineering
and geologic analysis of the other photographs showed the site to be underlain
by well-drained deposits of sandy loam. There was a possibility of encountering
some “perched water tables”—where a layer of impervious clay traps a small
quantity of water—but this was not considered a problem.
We also used a
newly developed electronic distance measuring system (EDMS). An agent faked a
flat tire on the side of the road by the aiming point. While working on the
tire, he placed a small device on the hood of the car. The device received and
transmitted data in the EDMS system. Thus, air photogrammetry and electronic
measurement fixed the coordinates of the target cables.
the supervision of a Berlin-based Corps of Engineers unit, the requisite
“warehouse” was constructed on the site, using mostly local contractors and
available materials. Keeping the plans secret was a constant challenge. Time
magazine reported that a civilian engineer had quit the construction project in
disgust because the blueprints seemed crazy. “Why build a cellar big enough to
drive through with a dump truck?” he asked.  Good point. Warehouses were usually built on
reinforced concrete slabs poured on well-drained, compacted sub-bases. A
warehouse with a basement normally would require columns and beams, which were
not incorporated into our plans. Our intention was to use the basement for the
storage of the excavated soil, so columns and beams ultimately would not be
necessary. The civilian engineer who quit was not the only one to raise an
eyebrow. The Army Chief of Engineers finally resolved the design controversy.
Calling it an “experiment,” he ordered the warehouse built as planned, with a
basement and no columns and beams.
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From Training to Action
British sappers who would play a key role in the tunnel construction were
invited to the New Mexico test site to observe the operation of the shield in
conjunction with the liner plates. The time had come to demobilize the test
site and ship all of the equipment to Berlin. The last step was to pack up all
of the unit’s files—consisting of requisitions, receipts, and disbursements—for
shipment to CIA headquarters, where they were locked in a safe.
All along, Les
had planned to send the equipment to a US Army Quartermaster Corps boxing
facility near Richmond, Virginia, for final packing for shipment to Berlin. Now
he discovered that the boxing plant was due for closure and he quickly had to
negotiate a 30-day hold. At Richmond, the metal parts were sprayed with a
rubberized compound to eliminate clanking as they were taken into the tunnel
and assembled. We wanted to avoid any kind of cowbell chorus deep in the
tunnel. The shield, liner plates, conveyor belts, and a small, battery-powered
forklift were shipped to Hamburg, Germany. From Hamburg, this most secret cargo
was transported to West Berlin on an ordinary goods train—no armed guards or
security arrangements of any kind. The cargo arrived in West Berlin without
The dig began
in August 1954. A 10-foot-diameter vertical shaft, 10 feet deep, was excavated
15 feet inside the warehouse foundation. The shield was assembled in this shaft
below the basement floor. The excavation of the tunnel started with a sequence
of push, dig, retract, assemble liner-plate ring, and repeat. An unanticipated
messy problem developed about 10 feet beyond the tunnel portal when the shield
passed under the leach field of the compound’s sanitary system. The drainage
problem was quickly solved with a pump. History does not record what was used
to alleviate the odor!
- Tunnel interior with wooden rails for forklift and sandbag 'benches' for utility lines and ventilation.
proceeded. A wooden-rail track was built to keep the forklift on course. About
one-eighth of the spoil never left the tunnel. Sandbags were filled and stacked
halfway up the sides of the finished tunnel. They were secured with steel
cables and gave the tunnel cross section a T-square look. The benches formed by
the sandbags were used to support and store air-conditioning ducts and power
and message cables running back and forth between the equipment-room amplifiers
and the Ampex recorders, which packed the first floor of the warehouse.
of the shield resulted in an overcut of 2 1/ 2 inches. This provided space for
the liner plates, but left a 1/2-inch void between the tunnel and the
undisturbed earth above. This void had to be filled in order to prevent
subsidence of the earth above the tunnel. About every fourth liner-plate ring
had “grout plugs,” threaded cores that filled holes used for pumping grout into
the void. The plugs were screwed out, grout under high pressure was pumped in,
and then the plugs were replaced. The grout selected was called “Vollclay,” a
molecular composite of clay, minerals, and other ingredients. Once, a full
boxcar of Vollclay disappeared between Chicago and Baltimore! It took five days for the Office of Logistics
to find the shipment, but the grout reached Berlin without delaying the
progress on the tunnel.
team of sappers started—and completed in the spring of 1955—the construction of
the vertical shaft needed to gain access to the Soviet communications cables.
This was the most delicate and tedious job in the entire process. The vertical
shaft was carved out using a “window blind” shield: A slot was opened and about
an inch of soil was removed; then that slot was closed and the next one opened.
This sequence was repeated until the target cables were reached, a process that
required extreme patience and skill.
The tap of the
first cable was completed in May 1955. A team of British specialists started
the work of transferring the cable voice and signal circuits to the recording
equipment. The full tapes were collected and sent to London and Washington.
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occasions, I was invited to visit the tunnel site. I declined, suggesting that,
without a good reason for such a visit, we might be turning the tunnel site
into a tourist attraction. Then, a good reason surfaced.
equipment room, located under the roadway, was jammed with amplifiers,
transformers, and tuners. All of these devices used vacuum tubes—“valves,”
under British nomenclature—that were high heat generators. The maximum expected
heat load of these generators had been used to calculate the required level of
air-conditioning. Something was wrong, however, because the temperature in the
equipment room was rising.
had to be solved before winter set in. Some cold morning, a frost-free black
mark might appear on the roadway over the equipment room, perhaps extending
into the field between the road and the warehouse, calling attention to
something strange occurring below the surface. Emergency action was needed.
chilled-water air-conditioning system was the only solution because there was
no room for extra ducts on the sandbag benches. Such a system, including about
1500 feet of newly developed 3/4-inch plastic irrigation tubing, was shipped to
the site. The tubing fitted nicely alongside the existing air ducts.
We still needed
a way to monitor the temperature in and above the tunnel. With assistance from
the Office of Logistics, we checked out a company in New Jersey named Wallace
and Tiernan Products, Inc. Primarily a manufacturer of altimeters and surveying
equipment, the company also made a remote temperature recording system
consisting of sensors, a data-recording station, and connecting cables. We
purchased the system and shipped it to Berlin.
Washington “expert,” I followed with an engineering drawing of the planned
locations and elevations of the sensors that were to go into the earth above
the tunnel. The first job was to install the sensors, since the plan called for
statistical analysis to determine if observed differences in temperatures were
random or significant. The grout plugs now had a second purpose. A number were
removed and holes were drilled in each to accommodate a sensor and its cable.
Eleven sensors were used: one in the tap chamber, four in the equipment room,
three in the tunnel, and three at the tunnel portal. The tunnel portal sensors
served as controls for comparative analysis. When the sensors were in place and
the plugs restored and sealed, the connecting cables were run back to the
The next step
involved getting the cables up through the basement floor of the warehouse and
connected to the recording station. This required pounding a hole through 16
inches of reinforced concrete with a star drill and hammer! It took three days before the cables were
connected and operating.
readings showed that the temperatures in the ground above the tunnel were in
general agreement with the readings from the sensors at the tunnel portal;
however, temperatures in the ground over the equipment room were indeed
elevated. Later, data sent to CIA headquarters showed that the temperatures
over the equipment room were dropping, almost certainly due to the supplemental
The completion of this demanding project is a tribute to the resourcefulness and expertise of an outstanding team of professionals.
Further monitoring of ground temperatures became irrelevant when the
tunnel was discovered in late April 1956. A team of East German telephone
workmen unearthed the tunnel while inspecting the cable system. That spring had
been unusually wet and we had overheard numerous conversations about flooded
cable vaults and the need to fix the problems and restore communications.
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years, the Berlin Tunnel project has been heatedly debated. Opinions have
ranged widely—some favorable, some resentful of its success, some political,
and many just plain wrong. Most of the controversy has centered on differing
interpretations of net intelligence value of this costly, time-consuming, and
technically challenging project. The simple truth, however, is that Leslie M.
Gross and his Army Crops of Engineers staff, along with the British sappers,
built the tunnel and tap chamber in SECRET!!
gentlemen, hand salute.
1. The author of this article served
in the CIA Directorate of Operations. The article, originally classified,
appeared in Studies 48, 2 (2004). It was reviewed and portions redacted
for declassification by the Historical Collections Division of the Information
D was a SIGINT component.
3. Accounts of the tunnel project covering its conception and
execution, its compromise by British spy George Blake, and Moscow’s delay in
closing it down include: David C. Martin, Wilderness of Mirrors (New
York: Harper & Row, 1980); Peter Grose, Gentleman Spy: The Life of Allen
Dulles (New York: Houghton Mifflin Company, 1994); David E. Murphy, Sergei
A. Kondrashev, and George Bailey, Battleground Berlin: CIA vs. KGB in the
Cold War (New Haven, CT: Yale University Press, 1997); and David Stafford, Spies
Beneath Berlin (Woodstock, NY: The Overlook Press, 2003).
magazine of 7 May 1956 reported that some Army people saw “friends whom they
knew to be engineers appearing in Berlin wearing the insignia of the Signal
5. A shield is made of a steel tube slightly larger
than the tunnel bore. Hydraulic jacks are fitted inside the outer rim opposite
the cutting edge. The shield, supported by an external framework, is assembled
in a shaft at the beginning of a tunnel. The shield then makes its first shove
forward, and the face is dug out until 12 or more inches of soil have been
removed. The jacks are retracted and liner plates are installed in the space
uncovered when the soil is removed. The flanges of the liner plates are bolted
to a reinforced concrete wall and then bolted to each other, completing the
first ring of the structure of the tunnel. The shield is then moved forward for
construction of the second ring.
7 May 1956.