The move of Station “C” to Corregidor represented the conclusion of several years of plans, negotiations, and construction.  The original idea of moving the Radio Intelligence Station, as it was then called, was apparently first conceived by CINCAF, Admiral Upham, and the Asiatic Communication Intelligence (COMINT) Officer, LT Wenger, in 1933.

Several years later, the Secretary of War informed the Secretary of the Navy that the Commanding General, Philippine Department had been authorized to begin work on the construction of the tunnel for the radio intercept station.  By August 31, 1939, the following three projects were identified as Project AFIRM, the Radio Intelligence Tunnel; BAKER, the Direction Finder Site; and CAST, the quarters of personnel of Station “C.”

Electronic Cypher Machine (ECM) Mark II came to into use at Station CAST in July 1941

In early October 1939, Project AFIRM was given the official title of “Navy Emergency Radio Station,” with the cover story that it was to “provide standby communications capability for Cavite and to conduct research in long distance reception with experimental equipment.”

On October 14, 1939, the mission at Cavite (Station “C”) began to move to Tunnel AFIRM.  During this move, Station “B” at Guam established watches to insure maximum coverage until the new “C” was operational.  The moved was completed three days later on October 17.  Once operational, the new station “C” at Corregidor reported the reduced Electromagnetic interference (EMI) allowed for better interception of communications that were not possible at Cavite.  Staff and equipment was increased when Station “A” at Shanghai was closed on December 10, 1940, giving the tasking and coverage of the Japanese Consular net to Corregidor.

The Corregidor tunnel had been designed and constructed especially for the unit with air-conditioning where the men performed COMINT work.  Two separate units had been established, a general unit for communications intercept and a “special crypto unit,” which included a Purple Machine to decipher Japanese Diplomatic traffic.  This unit also had IBM equipment, including an alphabetical tabulator, a card sorter, a punch, and a reproducing gang punch.  Those who worked in the communications intercept room probably had a SECRET security clearance and those who worked in the special crypto unit had TOP SECRET security clearance.

Intercept Operators and Analysts inside the tunel.

On December 7, 1941, just 51 days after Corregidor was operational, the Japanese attacked Pearl Harbor.  At the time of the Japanese attack, ten U.S. Navy officers and 51 enlisted men who had been trained in COMINT techniques were attached to Corregidor.

As the likelihood of the capture of Corregidor to the Japanese became more imminent, losing these 61 COMINT professionals became a matter of extreme concern to the leadership at the highest levels. These men represented a significant percentage of experienced COMINT personnel in the Navy. If they were captured and subjected torture and interrogation, the possibility of losing the intelligence advantage gained by seventeen years of study of Japanese code and ciphers would be a total loss!

A message (011500 of 1 February 1942) was sent from COMINCH to CINCAF, info COM 16 stated:

“Since withdrawal of Singapore unit to Colombo, Communication Intelligence organization under your command is of such importance to successful prosecution of war in Far East that special effort should be made to preserve its continuity.  Suggest consideration partial evacuation Fort Mills unit to establish new CI unit at [deleted] or Australian base communication intelligence.  See OPNAV seven seventeen fifty confidential.  Det will initiate shipment receivers and other equipment as recommended.  OPNAV has been informed.”

This was not the first message on the subject is evident from several other messages in the COMSIXTEEN War Diary between COMSUSAF and other commanders in the area which refer to specific plans for evacuation of personnel including personnel from “Special Fleet Radio Unit” as early as 28 January 1941.  Whether these were initiated by OPNAV or by CINCAF or they both independently set the wheels in motion, is not clear from material found in the war diary.

When word arrived to plan for evacuation of the COMINT personnel, the officers and enlisted were divided into four equal teams, each including technical and language officers, crypto yeoman and intercept radiomen.  This allowed each team to function as an independent intercept and processing unit.  The plan, when executed, was to evacuate each of the teams in phases.

Corregidor was attacked just after the attack on Pearl Harbor. The bombing destroyed the newly finished tennis court and handball courts, which the Japanese pilots probably misidentified for storage tanks as well as the water barge.  In order to get water to the tunnel, a water supply tank was pulled by tractor in between Japanese strafing attacks.  In all the attack runs no bombs damaged the tunnels and no one was injured, but all personnel moved from nearby topside quarters into the tunnels to eat and sleep. 

Radio intercept, direction finding and cryptanalysis operations continued almost uninterrupted. Radio communication with other stations, such as Washington (OP-20G) and Pearl Harbor (Station HYPO) also continued and made it possible to exchange technical data. 

Source: Jim Pearson, OTRG, NCVA