Maritime Fusion

Maritime Fusion is a San Francisco-based deep tech startup founded in 2024 that is building compact, high-temperature superconducting (HTS) tokamak fusion reactors purpose-built for marine and off-grid energy applications. The company's flagship product, called "Yinsen," is a 25-70 MWe fusion reactor designed to fit within a ship's hull (~6,000-7,000 m³), providing zero-emission propulsion and power for commercial shipping vessels and remote island energy installations without ever needing to bunker fuel. Unlike competing grid-scale fusion ventures, Maritime Fusion deliberately targets markets requiring ~15x less power than utility-scale plants, sidestepping unsolved materials science challenges such as first-wall heat flux and nuclear activation that hamper steady-state grid reactors. The company estimates first-of-a-kind unit costs at ~$700M in overnight CapEx, declining to ~$400M at scale, with a target first deployment in 2032.

The company's strategic insight is that the marine market - responsible for roughly 3% of global greenhouse gas emissions and with no viable decarbonization pathway - presents the ideal beachhead for first-generation fusion technology. By deploying at lower power densities, Maritime Fusion can operate within current materials capabilities while accumulating the operational learning needed to eventually compete at grid scale (targeting ~2040). Alongside its reactor program, the company is commercializing HTS cable assemblies for power distribution within fusion systems and marine electrical networks, creating a near-term revenue pathway. Maritime Fusion is also pursuing U.S. Department of Defense applications, including Ship-to-Shore mobile power plants in partnership with the Navy and DARPA, positioning it squarely within America's defense energy supply chain.

The founding team met at SpaceX - where they conducted radiation testing for Starship electronics - before reuniting at Tesla to work on Cybertruck and Optimus. Co-founder Justin Cohen is a nuclear engineer and plasma physicist with backgrounds at Columbia University, Princeton Plasma Physics Laboratory, and NC State. Co-founder Jason Kaufmann is a hardware and electrical engineer from the University of Pennsylvania with experience in AI hardware and rocket power systems. As a Y Combinator Winter 2025 company, Maritime Fusion represents one of the most credible early-stage fusion ventures targeting the maritime decarbonization and US defense energy supply chain, combining elite aerospace engineering talent with a pragmatic, market-first approach to commercializing fusion power.