I Wonder How Many of Those Soldiers We Saw Ever Came Back Alive?

We lived near Lake Nokomis when I was a child. I remember one summer day (it was '65, '66 or '67-we moved before the summer of '68) when the neighborhood families all went down to watch an Army helicopter hover over the lake. I recall, so vividly, how exciting it was for everyone to see the soldiers coming out of the helicopter, down the ladder and wade to shore. 

It wasn't until many years later, as an adult, that I realized those young men were practicing maneuvers before being sent to Vietnam. To this day, I wonder how many of those soldiers we saw on that sunlit summer day ever came back alive?