Bombing Attack of the trail system had begun Process_start on 14 December 1964 with the advent of Operation Barrel Roll .

`` Barrel Roll '' and the `` Secret Army '' attempted to stem Preventing_or_letting an increasing tide of People 's Army of Vietnam ( PAVN ) and Pathet Lao offensives .

`` Barrel Roll '' was one of the most closely held secrets and one of the most unknown components of the American military commitment in Southeast Asia .