Ya gotta remember, in those days, scuba as skindiving was basicly a man's sport.....ie: a man in athletic shape, good swimmer...three miles was the norm for qualification, calm and collected underwater......as there were no, octos, bc's to get them out of trouble or wetsuits that really were good fitting and warm.......
Guys routinely threw their tanks on over their head (there is a trick to that easy enough), had a bit of swagger, and refused to complain how cold the water was while their purple/blue skin turned back to normal.......ahhh the good old days!