In 1942, as part of the Manhattan Project scientists developed the first sustained nuclear chain reaction. Just nine years later, the first nuclear reactor able to generate electricity for use started up. For a time, it seemed like nuclear power was going to revolutionize global energy production, though soaring costs and questions over whether nuclear energy is safe and clean or not kept cooling towers from becoming ubiquitous. While not dominant, nuclear plants are still used to power electric grids around the world, including in the United States. Smaller reactors are also used to power certain ships.

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According to the World Nuclear Association, the U.S. Navy “has accumulated over 6,200 reactor-years of accident-free experience involving 526 nuclear reactor cores over the course of 240 million km” over the last 50 years. It’s easy to see why nuclear power is especially suited for seacraft. For one thing, compact nuclear reactors generate a lot of power proportional to how large and heavy they are when compared to other fuel sources. Size and weight are always an important consideration for ships.

Nuclear reactors also last a long time before needing refueling — nuclear-powered vessels can go over a decade before needing to refuel, making them efficient and independent. Newer cores in aircraft carriers are designed to last up to 50 years. The U.S. Navy includes 11 active nuclear-powered carriers. The vessel type is particularly well-suited for nuclear power because they’re so large and require a ton of power. However, there are other types of vessels powered by reactors and active today. Here’s four nuclear-powered ships that are not aircraft carriers.

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Submarines are probably more associated with nuclear power than any other vessel, including aircraft carriers. The first nuclear-powered sub — the USS Nautilus — was commissioned in 1954 as the Cold War arms race was really heating up. The vast majority of active nuclear-powered ships today are submarines, with 68 currently active in the U.S. Navy — in fact, America’s entire fleet of submarines are now nuclear-powered, with its final conventionally-powered sub decommissioned in 2007.

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Like in aircraft carriers, nuclear reactors are currently the ideal power source for submarines. While carriers require more power than subs, one of the main functions of the undersea craft is stealth, and the ability to go years without fueling is a huge asset for submarines. As part of the nuclear triad, in the event of a mass nuclear attack submarines would be the most likely to survive after initial strikes. They’d likely be in remote parts of the ocean and would be able to continue operations for an extended time in the aftermath of such a disastrous event.

This reasoning is why other countries also use reactors to power their submarines. The most advanced submarine in the Russian fleet is currently the Yasen-M, which is also one of the fastest attack subs in the world. It’s nuclear-powered, as is China’s Shang-class. The bulk of China’s submarine fleet is still powered by diesel, but the nation is currently building up its navy — with a focus on nuclear-powered craft. Similarly, the U.S. is modernizing its underwater fleet with the new Columbia-class nuclear submarine.

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While submarines are the most common nuclear-powered ships, the first surface vessel powered by a reactor was the Lenin, an icebreaker commissioned in 1959. It’s easy to guess what icebreakers are used for — they’re ships specifically designed to navigate through frozen seas. However, rather than cut through ice, icebreakers are built with rounded, extra-thick hulls that are designed to allow the vessels to ride up onto the ice — its heavy mass can then crack and break the frozen water.

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Icebreakers can be used as research ships, tugboats, support ships, exploration ships, and even luxury cruisers. As the planet heats up from the effects of climate change, the thawing of the Arctic is opening up new shipping routes as well as more accessible natural resources. This is becoming more strategically important by the day, and both the U.S. and Russia are shoring up their fleets of icebreakers. In 2020, the U.S. only had a single, aging icebreaker.

Russia is currently the only country with nuclear-powered icebreakers and has used them since the 1970s. In fact, in 1977 the reactor-powered Arktika became the first surface vessel to ever reach the North Pole. The modern Arktika icebreaker — completed in 2020 — is the largest model ever built. 

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Battleships dominated the seas during World War I and World War II, but now the vessel’s remaining legacy may just be the board game it inspired. Only two nuclear-powered battlecruisers survive today — Russia’s Kirov-class — and plans are to decommission one of them very soon. The two ships are the Pyotr Veliky and the Admiral Nakhimov, with the latter currently undergoing a refit to make it more suitable for modern battlefields. The Pyotr Veliky, called by Russia the world’s most powerful surface warship, was also supposed to be upgraded, but those plans were cancelled. Once the Admiral Nakhimov is seaworthy again, the Pyotr Veliky will be retired — leaving just one nuclear-powered battlecruiser still active.

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Both ships were commissioned in the late 1980s as two of four Kirov-class vessels. Nearly 40 years later, the Kirov-class battlecruisers are the largest currently-active surface combatants, if you don’t include aircraft carriers or amphibious assault ships. Displacing 28,000 tons, the two nuclear reactors, two steam turbines, and four propellers of the Kirov-class battlecruiser can generate up to 140,000 horsepower.

Shipping is vital to world trade, but only one active merchant ship today is nuclear-powered — the Russian vessel Sevmorput, which is planned to be decommissioned. However, other nuclear-powered civilian ships have operated before. The first civilian merchant ship to use a reactor was the Savannah, which was commissioned in 1959 as part of President Eisenhower’s initiative to show the public that atomic power wasn’t just useful for war. The Savannah is also the only nuclear-powered ship ever designed to carry civilian passengers.

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Its reactor-powered propulsion system could push the ship 20 knots and allowed the Savannah to cross 454,000 miles before needing to refuel. A conventionally-powered ship would need 28 million gallons of fuel to cover the same distance. Japan, and Germany also built nuclear-powered merchant vessels, but eventually these ships, like the Savannah, were retired. The more advanced power system required a larger, more specialized crew, which cost more money. The uranium-powered engines were also expensive to build and it was hard for companies to make their money back since the boats were fairly small and couldn’t carry a ton of cargo or passengers.

Furthermore, both the Savannah and Japan’s Mutsu freighter leaked radioactive material into the ocean, and nuclear-powered cargo ships ended up banned from many ports. Russia’s ​​Sevmorput — which is an icebreaker as well — may not be the last nuclear-powered merchant vessel, however. South Korea and Norway have both announced plans to build atomic-powered cargo ships. China has as well, claiming its thorium molten salt reactor-powered merchant ship will be the largest ever built.

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