As night ushered in a hushed silence over Vietnam’s Mekong Delta ... in a patrol boat as it cautiously made its way through the dense jungle along the perilous upper Saigon River.

Two Bell UH-1Bs, flown by the Navy’s lone helicopter attack unit in Vietnam, patrol the country’s south on a 1967 mission to support Navy SEALs. The Mekong ... of river patrol boats (PBRs).