In the episode where the soldiers take leave in Hawaii we see them walk to their plane at the end with a UH-60 Blackhawk helicopter sitting behind them. But this aircraft would not exist until the mid-1970s
Tan Son Nhut air base, the base camp for the second season, is depicted as a relatively quiet location set amongst woods and hills. In fact, it was - then as now - Saigon's international airport, and one of the busiest airbases in the world at the time. It is located in a heavily built-up area, with neither woods nor hills.