When nuclear energy was first harnessed, the US Navy became extremely interested in using it to power its fleet of submarines. Nuclear energy is perfect for submarines because:
A nuclear-powered submarine has a critical nuclear chain reaction going on near the center of the submarine. This boils water, which then goes through a turbine. The turbine is hooked up to a big drive-shaft that is hooked to a propeller on the back of the submarine. There are auxiliary turbines as well that are hooked up to electric generators to make electricity for the systems on the sub.
There are two main types of nuclear-powered submarines:
Ballistic missile subs (AKA “boomers”) are not only powered by a nuclear reactor, but they also carry a large amount of missiles with thermonuclear weapons for warheads. These submarines are supposed to just prowl around in unknown locations in the sea as a deterrent, so if someone nukes you, you can nuke them back from these subs and they’ll never be able to prevent you from doing so because you could be anywhere. In essence, these prevent people from nuking other people.
Fast attack subs are the hunter-killers of the sea. Their job is to hunt down and destroy other submarines or vessels. They’re fast and typically armed with things like Tomahawk missiles, and MK-48 torpedoes.
Nuclear propulsion worked so well for submarines that a few other vessels got nuclear engines instead of conventional diesels. Most notably, vessels like the Gerald R. Ford-class aircraft carriers have a few nuclear reactors powering them. The US Navy has had nuclear-powered cruisers as well, but does not have any now.
Russia operates a fleet of nuclear-powered icebreakers. A few nuclear merchant ships operated but none are in commission today. They would be an excellent way to reduce the emissions from the huge amount of international shipping that’s ongoing today.
Did you know? The NS Savannah was a nuclear-powered cargo ship that operated between 1962 and 1972. It’s deactivated now and moored at Pier 13 in Baltimore.
Commercial nuclear power plants evolved from naval nuclear reactors, and the main designs in use today making electricity (PWRs and BWRs) are direct decedents of naval reactors. Water coolant is really nice at sea because there’s a lot of cooling water. A lot of plant operators learned how to run nuclear reactors in the Navy.
Nuclear propulsion is well-suited for space travel and rockets, so that’s under development. The Russians did have some nuclear-powered tanks. Before intercontinnental ballistic missiles were developed, the US Air Force worked a lot on the Aircraft Nuclear Propulsion project to make a nuclear-powered long-range airplane. Various test reactors like HTRE-3 pictured here were operated in this project but no plane ever actually flew, so far, on nuclear power.
The only nuclear-powered cars you’re likely to ever see are electric ones charged by nearby nuclear power plants.