Y Combinator-backed Maritime Fusion Raises $4.5 Million From Trucks VC and Paul Graham

Maritime Fusion, building a first-of-a-kind fusion reactor for marine and off-grid applications, led by Justin Cohen and Jason Kaufmann, has secured $4.5 million in seed funding led by Trucks VC, with participation from Paul Graham, Aera VC, Alumni Ventures, Y Combinator, and others.

The HTS magnet lab in San Francisco is now operational, enabling rapid testing of prototype cables and magnets. A recent bench test carried 5 kA through the SHIELD HTS cable using liquid nitrogen as the coolant.

Work on Yinsen, a low–power–density HTS tokamak, is also progressing, supported by partnerships with Columbia University and the Department of Energy’s DIII-D National Fusion Facility for experiments aligned with the planned pulse scenario.

The patent-pending SHIELD cable has a cross-section smaller than a quarter (excluding the cryostat) and is designed to carry up to 8 kA at 77 K, with even higher performance under fusion-relevant conditions. A modular N×N architecture enables high engineering current densities while preserving thermal and mechanical robustness.

The design can be optimized for fusion with high-pinning HTS tape or adapted for lower-field power distribution, including AI data centers, by swapping the tape while keeping the rest of the structure unchanged. Innovations in lengthwise insulation and soldering techniques reduce AC losses and improve uniformity.

Equivalent copper busbars would require more than 2000 mm² of conductor and over triple the mass, while also suffering significant ohmic losses, compared with the HTS cable’s lossless operation and modest ~1.5 W/m cryocooling requirement at 77 K.