Today in History, December 11, 1961:
The first helicopters (H21C Shawnees) arrive in Vietnam, with the mission of transporting South Vietnamese troops into combat.
Helicopters had been used in Korea to transport wounded soldiers, but by Vietnam they had developed to the point that they could be used to move troops quickly into combat areas. This was a marked change in combat operations.
The decendants of the Shawnee would of course play an ever more important role in Vietnam and beyond.