vietnamwarera:

A North Vietnamese Army “roadblock” on Hwy 19, 1968.  All sorts of debris–sticks, cans, empty brass, etc–would be placed on the road during the night.  Because any object could be booby-trapped or hide a mine, this harassment tactic would delay the morning road opening–and sometimes would portend an ambush.  (3-C-1/69 Armor)

Submitted by a veteran.