Whoooooooo lives in a peanut under the sea? So-vi-et A-qua-nauts! It does look like a peanut, right? I mean what the fuck even is that? I guess given the time period it was designed similarly to their Soyuz spacecraft, which also consists of two mated sections that are roughly spherical.
The official focus of the Sadko-II mission was hyperbaric medicine. No doubt that was researched, but Sadko-II is recognizably just another step in the Soviet government's development of utilitarian small habitats which could be deployed on subsea communications cables and left there longterm, so the unlucky fellows inside could listen in on transcontinental conversations.
As you can see from the above image, the Soviet man in the sea program resulted in many different habitats of wildly different design. There's Chernomor-II at the bottom, largest of the lot. Sadko-II was closer in size and purpose to Cousteau's 2 man 'Deep Cabin'. Not a home, but an outpost, for a specific military purpose.
Sadko-II was certainly a two man structure as well, you couldn't have fit any more inside if you tried. One of them would listen to and judiciously record tapped audio while the other slept, then they would trade places like hot bunking on a submarine.
Of course these days this is a job we'd do with unmanned, AI driven machines. But the state of technology in the 70s was such that many tasks done today by computers had to be done by a couple of human beings in a tin can. All the early Soviet space stations served as manned spy satellites for example, using film(!) that was air dropped to Earth in a small capsule for development.
Photos of Sadko-II are rare, unsurprising given its age and that it was developed behind the Iron curtain. Consequently the only interior photo, and photo of the exterior while submerged that I could find are stock photos. I won't just post them here for fear of legal reprisal but I feel reasonably safe linking them:
Stock photo 1: Exterior, submerged
Sadko-II was submerged to a depth of 82 feet, about the same depth as Deep Cabin. Divers made excursions from Sakdo-II to nearly twice that depth however. The mission lasted ten days, including three spent decompressing at the end.
It was perhaps the most unusual of the Soviet habitat designs, and an interesting relic of the era in which a human presence was still needed deep underwater or in orbit to perform basic tasks like taking photographs or tapping communications cables that have since been automated. Part of the honestly regrettable trend of removing human explorers from the last unexplored frontiers in favor of robots because of the cost savings.
Anyway, stay tuned for more. There's still several Soviet habitats to get through.
Stay Cozy!