Hermeus Corporation is an American startup company designing a hypersonic airliner.
The company was founded in 2018 with initial funding led by Khosla Ventures.
In 2021, Hermeus secured $60 million in funding from the U.S. Air Force and venture capital to support the Quarterhorse flight test program.
In March 2022, the company raised a $100 million series B investment round led by Sam Altman. Other investors included Founders Fund, In-Q-Tel, and existing investors Khosla Ventures, Canaan Partners, and Bling Capital.
The Quarterhorse aircraft under development is planned to reach Mach 5 with a range of . The company claims to have designed, built, and successfully tested a Mach 5 engine prototype. In August 2020, Hermeus received a $1.5 million contract from the United States Air Force to develop their proposed aircraft and function as a possible Air Force One.
They are building the supersonic Quarterhorse Mk 2 with an advanced engine based on the Pratt & Whitney F100. Quarterhorse Mk 2 is expected to hit speeds greater than Mach 2.5.
The engine adds a precooler to a standard Pratt & Whitney F100. The precooler lowers the temperature of incoming air, preventing the melting of engine parts and allowing the engine to be more efficient.
The Chimera engine is a turbine-based combined cycle machine that combines a pre-cooled turbine with a ramjet. It was successfully tested in November 2022. It is planned to power the Quarterhorse Mk 3, which will reach speeds close to Mach 1. Upon reaching sufficient speed, Chimera routes incoming air around the turbojet and the ramjet takes over at around Mach 3.
The Quarterhorse development program has four stages:
Darkhorse is an uncrewed hypersonic military jet intended for mass production.
In August 2024, Hermeus completed low-speed taxi tests, and in May 2025 the Quarterhorse Mk 1 flew a successful flight test at Edwards AFB. At the same time it was reported that the Mk2 was already well into its manufacturing process.