sentences:  He sailed to Vietnam with the 1st Cavalry Division (Airmobile) and served a one-year tour, nine months with the "First Cav", the last three months with the 48th Aviation Company.Mason spent his first month in Vietnam clearing land for his unit's airbase, after which he and his fellow pilots flew many missions to resupply the infantry and pick up wounded.At that time 1st Cavalry Medevac helicopters were not allowed to fly if the landing zone was hot.