There was a very small presence of Americans in South Vietnam at the time - around 5,000. Mostly US government workers (e.g. USAID), CIA and some military. Wh

There was a very small presence of Americans in South Vietnam at the time - around 5,000. Mostly US government workers (e.g. USAID), CIA and some military. When the US disengaged in 1973, it left most of the military equipment and gave it to South Vietnam. So most of the helicopters and such that fled to the US fleet were South Vietnamese aircraft, not US aircraft. So I assume the US has pretty much written them off before that.