>>99500569>>99494504This. SEALAB I was constructed in 1964, in fact. By the 1970s it was not a new thing at all. Before that, Jacques Coustau had his ConShelf stations running (funded by private finance); there were numerous others, all competing to discover new diving techniques, explore the seabed, etc etc.
Wikipedia (unsurprisingly) has a writeup of most:
https://en.wikipedia.org/wiki/Underwater_habitatBut most of them are defunct because they either achieved their aim (they were after all science stations, not hotels) or became superfluous as other projects achieved the same goals.
NASA's NEEMO project has been running continuously since 2001, and is used as a training station for astronauts (being the closest you can get to simulating the effects of being stuck in a space capsule for extended periods and needing breather equipment to leave it without going to actual space). And you can stay in a number of underwater hotels around the world, if you're a rich cunt.
