This startup wants to build a fusion reactor — on a boat

Maritime Fusion, led by CEO Justin Cohen, is setting its sights on a groundbreaking initiative: constructing a fusion reactor aboard a ship. While this may sound ambitious, advancements in artificial intelligence and superconducting magnets are bringing fusion energy closer to commercial viability. The industry is increasingly optimistic, suggesting that it's a matter of when, not if, fusion energy will be realized. Fusion energy promises to provide vast amounts of clean power from abundant water resources, and placing a reactor on a vessel is not as far-fetched as it may seem. Nuclear fission-powered submarines and aircraft carriers already operate silently and efficiently in the oceans, demonstrating the feasibility of nuclear power at sea. In fact, there were discussions in the 1960s and 1970s about using nuclear power for cargo ships. Cohen remarked, "Fission has definitely paved the way in terms of nuclear power on ships." Fusion offers the potential for similar benefits without the risks associated with meltdowns or radiation. Currently, most efforts in the fusion sector are focused on land-based reactors. However, Maritime Fusion is uniquely exploring the concept of placing a tokamak—a leading fusion reactor design—on a ship. Cohen believes that if fusion technology succeeds, the company could gain a significant advantage by venturing into marine applications early. Additionally, he notes that operating at sea might have economic advantages; the cost of the initial fusion power plants will be substantial, and competing with solar and wind energy on land will be challenging. "At sea, the economics look different," Cohen explained. He highlighted the high costs of alternative fuels like ammonia and hydrogen, which could position fusion as a competitive option for powering cargo ships. To advance its vision, Maritime Fusion has secured $4.5 million in seed funding, led by Trucks VC, with contributions from Aera VC, Alumni Ventures, Paul Graham, Y Combinator, and various angel investors. The startup is part of Y Combinator's winter 2025 cohort. Maritime has begun the assembly of high-temperature superconducting (HTS) cables, sourced primarily from Japanese suppliers. These cables will be crucial for creating the powerful magnets necessary for the tokamak to confine plasma for fusion reactions. Additionally, they will provide a revenue stream as the company develops its power plant. The anticipated first fusion power plant, named Yinsen, is expected to generate around 30 megawatts of electricity. Cohen acknowledges that significant engineering challenges lie ahead, particularly in designing the systems that will harness energy and maintain the tokamak's operations. To streamline onboard processes, some tasks, such as fuel processing, will be conducted onshore. The initial Maritime tokamak will measure approximately eight meters across, with plans for it to become operational by 2032 at an estimated cost of $1.1 billion. In contrast, Commonwealth Fusion Systems (CFS) is working on Sparc, a smaller tokamak, and has raised nearly $3 billion for its demonstration plant, set to be operational next year. While CFS has a significant lead in the fusion race, Cohen remains confident that Maritime Fusion can carve out its niche. "We’re not going to spend billions on a breakeven-style device that doesn’t produce energy on the grid," he asserted. The goal is clear: the first tokamak will be designed to produce energy for customers, marking a substantial step forward in the pursuit of fusion energy.