Australian advertisement from Jantzen swimwear 1951, Be Attractive While You're Active. Love that headline. What's 'dramatically different' in 1951? Marina Match-mates, matching swimwear for you and your partner, that's what. NEW from Jantzen.
But wait,
This advertisement from Jantzen touting matching swimwear appeared in 1950, most likely in the US. So either:
A) Matching swimwear style started in the US and then got marketed in Australia, or
B) The rollout launch was a success and they decided to take it worldwide, or
C) The media but was made at different times in different locations, or
D) The seasonality made it more appropriate to launch later.
Who know, but I find these types of details intriguing. Either way, it's safe to say, matching swimwear ensembles began in the very early 1950s.