Jordan Bramble's Antares raises $470M for U.S. military microreactors
Paradigm and Caffeinated co-led $370M in equity, while $100M in debt backs a 2027 power test and targeted 2028 deployments.
By Ryan Merket · Published
Why it matters
Antares has moved beyond a paper design, but its $470 million bet still depends on converting a zero-power test into licensed, repeatable electricity production.
Jordan Bramble's Antares has raised $470 million, capital for Antares' next step after reactor criticality: producing electricity and installing microreactors at U.S. military bases.
The Series C includes $370 million in equity and $100 million in debt, according to Antares' July 27 announcement and TechCrunch. Paradigm and Caffeinated Capital co-led the financing, with Point72 Ventures, Shine Capital and Industrious Ventures participating. Antares says it has now raised more than $600 million since its 2023 founding. The announcement includes no valuation, debt provider or debt terms.
Bramble founded Antares with Julia DeWahl, who serves as a co-founder and board member. Bramble's route into nuclear hardware ran through software, government and food technology. He previously co-founded Local Kitchens, worked in engineering and data roles at companies including CAVA and Opower, and served in the White House Office of Management and Budget and the U.S. Digital Service. His public biography lists a B.S. from George Mason University and a master's degree from Georgetown.
DeWahl brought a different operating background. Her personal site says she worked on Starlink at SpaceX and previously worked at Opendoor. Together, Bramble and DeWahl built Antares around the premise that defense installations and space missions could become the first customers for factory-produced reactors that are smaller and easier to transport than conventional nuclear plants.
The round shifts Antares from a reactor-physics milestone toward the harder commercialization work.
Criticality was the starting line
Antares' Mark-0 reactor reached criticality at Idaho National Laboratory on June 4, sustaining a controlled nuclear chain reaction under the Department of Energy's Reactor Pilot Program. DOE described the result as an advanced-reactor criticality milestone.
Mark-0 did not produce electricity. A DOE environmental review described it as a zero-power experiment without power-conversion or heat-removal systems. As RuntimeWire reported after the test, the result validated reactor physics and control behavior while leaving the power system, licensing work and commercial deployment ahead.
Antares plans to test Mark-1, an electricity-producing reactor, in 2027. Initial defense deployments are targeted for 2028. Both dates remain Antares targets, and missing either would push out the point when the newly raised capital can begin supporting operating assets rather than engineering milestones.
The R1 design is intended to generate between 100 kilowatts-electric and 1 megawatt-electric for more than six years between refueling, according to Antares. It uses TRISO fuel particles inside a graphite core, sodium heat pipes for passive heat transfer and a closed nitrogen Brayton cycle to convert heat into electricity. Integrated shielding and a transport cradle are meant to let Antares manufacture much of the system away from the deployment site and then connect it to a local microgrid.
Antares has also invested in bringing manufacturing under its own roof. Antares previously described its Torrance facility as a 145,000-square-foot vertically integrated research and development site; it later said Antares Prime was expanding to 322,000 square feet. Antares separately says it precision-machines nuclear-grade graphite in house. Vertical integration gives Bramble tighter control over iteration and supply, though it also makes the $470 million round partly a factory-financing bet in an industry where each technical milestone carries regulatory and construction risk.
The Air Force provides a first market
In April, the Department of the Air Force paired Antares with Joint Base San Antonio under the Advanced Nuclear Power for Installations program. Radiant Industries was paired with Buckley Space Force Base, while Westinghouse Government Services was paired with Malmstrom Air Force Base.
The Air Force describes those sites as potential locations. Joint Base San Antonio still requires siting and environmental analysis under the National Environmental Policy Act, and Air Force materials set a program goal of operating at least one reactor by 2030 or sooner. Antares' 2028 deployment target is therefore an earlier internal schedule rather than a completed procurement commitment.
Antares has not published the number, value or full customer list for any reactor orders. The Joint Base San Antonio program is publicly documented, but it has yet to establish an operating commercial reactor or publicly verifiable revenue.
Commercial licensing also remains ahead. The Nuclear Regulatory Commission lists Antares in pre-application activities that began in May 2025. That engagement is an early regulatory phase rather than an issued construction or operating license.
Investors are financing the deployment race
The size of Antares' round reflects how quickly capital has moved into transportable nuclear systems with defense and data-center applications. Radiant, Antares' closest venture-backed peer in portable reactors, raised more than $300 million in December 2025 to build manufacturing capacity and prepare its Kaleidos reactor for testing. Established nuclear suppliers such as Westinghouse and BWXT are pursuing the same federal demand with existing supply chains and decades of nuclear operating experience.
Antares enters that competition with a completed criticality experiment, an Air Force pairing and a design built around a narrow initial customer: military installations that need continuous power when the surrounding grid fails. That focus gives Bramble a defined procurement path. It also concentrates Antares' near-term outcome around federal schedules, safety reviews and the ability to turn Mark-0's reactor-physics result into a power-producing machine.
The Series C buys time, equipment and manufacturing capacity for that conversion. Antares still has to demonstrate the part customers ultimately purchase: years of safe, reliable electricity from a reactor that can be built repeatedly, transported and operated at a defended installation.