Sealab I was the US Navy's first underwater habitat. It proved the concept of mixed gas saturation diving. In 1964, 4 divers lived at a depth of 200 feet for 11 days. It is now an exhibit at Panama City's Man in the Sea Museum. They have a Gofundme site to collect money to refurbish this piece of diving history. The link is here.
Here is an old documentary about the project.
There were other underwater habitats that followed Sealab I. There was Sealab II and then Tektite but they have all been lost to the scrapyard. Please send something to save Sealab I.