Fusion Power for the Open Sea

The shipping industry accounts for nearly 3% of global greenhouse gas emissions, and unlike the grid, it has no clear path to electrification at scale. Maritime Fusion is betting that compact fusion reactors — not batteries, not green ammonia — are the answer. The company is building a tokamak-based fusion reactor specifically sized and hardened for commercial ships and remote off-grid applications.

Founded by Justin Cohen and Jason Kaufmann, both veterans of Tesla and SpaceX, Maritime Fusion emerged from Y Combinator's W25 batch with $4.5 million in seed funding led by Trucks VC. The round also included notable investors Paul Graham, Alumni Ventures, and Aera VC.

What They're Building

The company's reactor, named Yinsen, targets approximately 30 MWe of output from a roughly 8-meter diameter form factor — compact enough to fit in a large vessel's engine room. Maritime Fusion is pursuing the maritime and off-grid markets deliberately: these sectors need less power than the grid and represent a more forgiving commercial path to first-generation fusion deployment.

A key enabling technology is their SHIELD cable — a high-temperature superconducting (HTS) cable that achieved 5,000 amps in bench testing. Superconducting magnets are central to tokamak performance, and SHIELD gives Maritime Fusion a near-term commercial product while the reactor program matures. The company has a Sponsored Research Agreement with Columbia University and is working with the DOE's DIII-D National Fusion Facility on plasma physics development. They are targeting the reactor to be operational by 2032.

Why Maritime First

Grid-scale fusion faces an enormous bar: it must compete on cost with solar, wind, and existing baseload generation. Maritime and off-grid applications have a different calculus — fuel costs are high, infrastructure is scarce, and zero-emission mandates are tightening. A fusion reactor that works reliably at sea doesn't need to be the cheapest kilowatt-hour in the world; it needs to beat the alternatives available in the middle of the ocean. This market insight is what makes Maritime Fusion's approach strategically distinct from the many grid-focused fusion programs.