Y Combinator-backed Maritime Fusion Raises $4.5M From Trucks VC, Paul Graham

Founded by ex-Tesla engineers, Maritime Fusion combines high-temperature superconducting (HTS) cable technology with DOE and Columbia Research partnerships to bring fusion energy to ships.

SAN FRANCISCO, Nov. 24, 2025 /PRNewswire/ -- Maritime Fusion, a fusion energy company developing first-of-a-kind (FOAK) reactors for maritime and off-grid applications, today announced the closing of a $4.5 million seed round led by Trucks VC, with participation from Silicon Valley legend Paul Graham, Alumni Ventures, Aera VC, Y Combinator, and several strategic angel investors. The capital accelerates the company's mission to develop its HTS cable technology and bring fusion power to the commercial shipping industry before grid-scale adoption.

While most fusion companies aim directly for grid electricity production that requires high power density and a large capacity factor to be cost competitive, Maritime Fusion is taking a different approach. The company is developing a low-power-density tokamak reactor optimized for off grid applications, where the first viable commercial use cases require 10× less power with zero emissions, far lower uptime requirements, and cost parity with alternative energy sources. This approach to commercialize the tokamak also alleviates the main unsolved materials science and confinement challenges that emerge between breakeven fusion and grid scale reactors.

"Breakeven fusion is on the horizon, but the grid may not be the first place fusion achieves commercial success" said Justin Cohen, co-founder and CEO of Maritime Fusion and a former Tesla engineer. "By targeting applications that require lower power and lower uptime, we simultaneously reduce challenging physics problems from power exhaust to nuclear activation, while also decreasing the burden and cost impact of maintenance operations that are unavoidable in any first-of-a-kind deployment."

Maritime Fusion is developing Yinsen, a low-power-density HTS tokamak designed with an emphasis on reducing the scope between breakeven class devices and grid scale reactors. The company is advancing the physics basis for Yinsen through two research relationships:

• A Sponsored Research Agreement with Columbia University, focused on pulse scenario development and time dependent plant systems.
• Participation in the U.S. Department of Energy's DIII-D National Fusion Facility, enabling targeted experiments aligned with Maritime Fusion's operating regime.

Maritime Fusion has launched a high-temperature superconducting (HTS) cable program centered on its patent-pending SHIELD (Superconducting High Integrity Energy Link & Distribution) architecture. The cable recently reached a major milestone, carrying 5,000 amps at 77K in a liquid-nitrogen-cooled bench test at the company's new San Francisco HTS lab.

SHIELD has a smaller diameter than a quarter (excluding cryostat hardware) but can handle up to 8,000 amps at 77K self-field and even higher current under fusion-relevant conditions. The architecture is also highly modular, allowing for easy packaging of an array of insulated cable bundles to enable industry-leading engineering current densities, strong mechanical robustness, and simplified integration into fusion magnets. 

While SHIELD is the heart of Maritime Fusion's tokamak magnets, the company also plans to sell this same cable into commercial power distribution sectors starting with AI datacenters, where demand for dense high-power transmission is growing rapidly. Compared to copper material, an HTS solution offers enormous energy savings by avoiding ohmic losses, requiring only ~1.5 W/m of cryocooling at 77K. The main difference in the fusion grade cable compared to power distribution is the need for REBCO tape with Advanced Pinning for high field fusion applications, but nearly all other features of the cable are otherwise the same. The value of efficient power transfer coupled with a much smaller physical footprint enabled by HTS conductors, can exceed $10M per year in cost savings for large-scale datacenter operators.

"Fusion's impact on transportation will be enormous, obviously for the grid, but also for large-scale applications like maritime," said Jeffrey Schox, partner at Trucks Venture Capital. "The team picked a smart first channel, allowing them to make a significant impact well before the largest barriers to grid fusion are fully solved."

Maritime Fusion is hiring across engineering, manufacturing, and business development.
Candidates can apply here.

About Maritime Fusion

Maritime Fusion is developing HTS cable technologies and a low-power-density fusion reactor designed for off-grid applications. Founded by former Tesla engineers, the company is headquartered in San Francisco and backed by Trucks VC, Paul Graham, Alumni Ventures, Y Combinator, Aera VC, and leading deep-tech investors.

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SOURCE Maritime Fusion