Your question is a very valid one and deserves a valid answer..Not nonsense or cute remarks...
Wet suits were introduced in the spring of 1953 or was it 1954?
There was a question at that time in the small diving community about under garmets. Some used them some didn't. There were several reasons for not wearing them,
1) The bathing suits of the 1950s were very full cut and very baggy and were difficult to stuff int the suit. They tended to bag up and create wear points etc.
2) It was thought that it was colder by a factor of several degress with a suit on under the wet suit. However to my limited knowledge no test were ever performed on heat loss.
On dive boats most used the small French cut suits of the era. These were introduced to the US diving community by the late great French explorer and inventor Dimitri Rebikoff in the ealy 1950s. Poor Dimitri has all but been ignored and almost forgotten by the diving world yet he gave us so much.
The limited number of women in the sport at that time, including my wife dove with womens underwear, Bra & panties. I often dove with nothing under the wet suit.
The Speedos were introduced to the US from Australia in about 1965 and became the undergarment of choice for most divers for in water use.
LA County, which was the only certifing organization at that time had a code of wearing for wearing Speedos. The deck teaching uniform for the male and the few female instuctors was red boxer swim trunks over any color speedo. When diving in the pool or ocean in wet suit most reverted to the Speedos only.
Hope this helps..
SDM