While the fusion industry races to build the first commercial reactor on land, Maritime Fusion just raised $4.5 million to take a completely different approach - putting tokamak reactors on ships. The Y Combinator startup believes maritime deployment could solve fusion's biggest commercial challenge by targeting expensive maritime fuels rather than competing with cheap solar and wind power.
The fusion startup landscape just got a nautical twist. Maritime Fusion closed a $4.5 million seed round to develop what CEO Justin Cohen claims is the first serious attempt at putting a tokamak fusion reactor on a ship. The round was led by Trucks VC with backing from Aera VC, Alumni Ventures, Paul Graham, and Y Combinator, where Maritime was part of the winter 2025 batch.
The concept isn't as outlandish as it sounds. Nuclear-powered submarines and aircraft carriers have been prowling the seas for decades, operating quietly for years between refueling. The civilian maritime sector even experimented with nuclear cargo ships in the 1960s and 70s. "Fission has definitely paved the way in terms of nuclear power on ships," Cohen told TechCrunch in an exclusive interview.
But Cohen's betting fusion offers something fission can't - massive clean power without meltdown risks, proliferation concerns, or radioactive waste. More importantly, he thinks the economics work better at sea than on land. While fusion struggles to compete with cheap solar and wind on the electrical grid, maritime fuels tell a different story. Ammonia and hydrogen - the leading candidates to replace diesel in cargo shipping - cost enough that first-generation fusion reactors could actually compete.
"Those are some of the other really expensive fuels that might actually be the only other things that are as expensive as first-of-a-kind fusion," Cohen explained. "In those cases, we actually do compete, just straight up."
Maritime's already moved beyond PowerPoint presentations. The company is assembling high-temperature superconducting cables from Japanese-supplied tape, building the foundation for the powerful magnets needed to confine fusion plasma. These cables will generate revenue by selling to other companies while Maritime develops its main reactor.
