The ocean is an inhospitable place for soft, land-based human bodies. It's dark, oxygenless, and, perhaps most intractable of all, really cold. At the pressure of certain depths, neoprene suits will compress and lose their insulating power. The air in tanks also gets cold, so divers become chillier with each breath. But in the 60s, the Navy thought they had an ingenious solution to it all: nuclear power.
In a blog post on Medium, Steven Meintz, lays out the long, fraught history of the cold wetsuit, in which the most fascinating development is the radioisotope swimsuit heater. In the 60s, the Atomic Energy Commission (AEC) was trying very hard to prove that nuclear energy was good for more than killing people. It ended up helping the Navy create a wetsuit powered by plutonium-238.
Plutonium-238 is a byproduct of nuclear weapons production, but it also happens to be the ideal nuclear fuel for wetsuits—once you accept a nuclear-powered wetsuit is a good idea in the first place. It emits a lot of radiation, but only the kind that is easy to shield from. In this wetsuit design, almost a kilogram of plutonium-238 is placed inside a canister, where it radiates heat to a series of fluid-filled tubes lining the suit.
When the Navy actually tested the suit, it did not... work so well. "It is concluded that the system in its present state is incapable of maintaining thermal balance in a diver at depth, and its use under SEALAB III conditions would entail a grave risk of hypothermia," Navy researchers wrote. As the Atomic Skies blog points out, this may be because the Navy couldn't get enough plutonium-238.
Indeed, the radioactive isotope is hard to come by—and even harder to come by now that the U.S. is no longer making nuclear weapons. Today, plutonium-238 is still used to power space probes like Voyager and Curiosity traveling in the cold, dark parts of our solar system (and beyond). Even NASA's stockpile is rapidly running out, and they've just restarted a $50 million program to make 1.5 kilograms of plutonium-238 year. It would have been one expensive, warm wetsuit.
Images from Atomic Energy Commission Report via Atomic Skies