This message form, used to pass four figure encrypted voice messages, was captured at Binh Tram 33, on Route 9 near Tchepone, Laos.

Probably one of the most dramatic stories that has never before been declassified and told had to do with signals intelligence of the movement of men and materiel down the Ho Chi Minh Trail from North Viet Nam through Laos and Cambodia and then into South Viet Nam.

Throughout the earlier years when GEN William C. Westmoreland was still in command, estimates of the enemy’s infiltration down the trail were just that — estimates. Efforts to track and calculate the enemy’s movement of men and units were both difficult and controversial. Often there was a lag of months before intelligence officers could identify with any assurance the number and destination of those who had come down the trail, building up this picture from painstakingly assembled prisoner-of-war interrogations, captured documents, and agent reports. 

This frustrating situation was dramatically, almost magically, swept away just at the beginning of GEN Abrams’ tenure by acquisition of a new and remarkably accurate means of determining details of enemy movements south. U.S. intelligence began to intercept, break, and read encoded enemy radio traffic that accurately and consistently reported the numbers, progress, and destinations of infiltration groups moving down the Ho Chi Minh Trail.

Traffic on the trail was controlled by the General Directorate of Rear Services (GDRS) in Hanoi and administered by a Commo-Liaison Bureau through a series of military way stations, known as binh trams, at intervals along the route. Each station was numbered and, therefore, individually identifiable. Binh Tram 33 in Laos, for example, was in the vicinity of Base Area 604 near Tchepone. The system of binh trams, later further expanded, extended initially from Hanoi through North Viet Nam and Laos to the tri-border area where North Viet Nam, Laos, and South Viet Nam meet. 

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