In the 1930's sun bathing became more popular as an inexpensive recreation. Athletic swimming and synchronized swimming was also popular. The suits reflect the need to show more skin to the sun and be more streamlined for water sports. Belted maillots were popular with boy cut legs or slim skirts. The exposed v-back was invented and a few daring ladies even exposed their midriffs with the first bikinis. The suits above are from a 1930's catalog. I love the red and white striped one on the right!
Jean Harlow striking a pose. Her suit is very glamorous for the time and shows a lot of skin.
Beach athletics. Notice her V-back and belted waist.