Huey helicopter, for infantry transportation.
Helicopters usage gave to the infantry movement skills they had never had before, and the Vietnam war was fought using brand-new tactics.
The first Vietcong attacks against US forces were some plainly suicidal missions, with the only goal of giving the Vietnamese generals some intel about the real US capabilities, with the purpose of planning a strategy for the future.
The Huey helicopter used to mount two machine guns each side, operated by hands (but they couldn't fire straight in front of the vehicle).