Before arriving in South Vietnam, the USAFSS had an opportunity to test this contingency plan during the Laotian crisis of early 1961. It did not work out very well.
The AFSS had been asked to support JTF-116. However, the JTF liaison lacked an understanding of SIGINT and did not grasp the operational requirements for immediate movement of the operational vans; only the transport of the AFSSO communications van was approved.” Specifications for the airlift of the entire CCU had been underestimated. The alert had gone out to AFSS personnel over the Pacific rim, who then found themselves in the limbo of hurry up and wait” as alerts went on and off as the situation in Laos fluctuated.
Among other problems, the long flight time needed to arrive at an orbit suitable to intercept the airlift communications cut down on actual mission time, while poor atmospherics often hampered VHF hearability. The handful of available aircrews took a pounding from the extended missions aloft and in a short time were exhausted. The air force was to learn, as it did later with the Hilo Hattie program in South Vietnam, that ACRP mission plans needed to be written with actual conditions in mind. [ — ]
On 20 December 1961, PACAF Advised [ — ] that it was sending a 350-man team to man to establish a Tactical Air Control System (TACS) under Project Barn Door to Vietnam. (Barn Door was an USAF project to upgrade the forward air control system (FAC) in South Vietnam.) This contingent included the CCU, which would be limited to fifty men. The following day, the wing advised PACAF that it would deploy one intercept van, one cryptanalytic van, one analysis van, one high frequency direction finding (HFDF) station, and a set of support vans and vehicles. At the same time. [ — ] advised PACAF that it was sending a communications van to Tan Son Nhut Air Base to support the AFSSO serving the USAF’s 2nd Advanced Squadron (ADVON). The wing also sent along additional intercept and analysis vans to Tan Son Nhiit in case there was an expansion of the mission. In large measure, the air force’s deployment matched the contingency plan it had written up the year earlier.
The mission for the CCU was to provide VHF intercept coverage of communist air forces operating in the area of western DRV and eastern Laos – where most of the communist air supply flights operated – and to alert the 2d ADVON [ — ] deploy to the region. In this, the CCU was heavily dependent on the USAFSS site in the Philippines for tip-offs to incipient communist flight activity.
Source: Spartans in darkness: American SIGINT and the Indochina War, 1945-1975