California, USA-based startup Hermeus has flown its Quarterhorse Mk 2.1 uncrewed test aircraft at supersonic speed for the first time, reaching Mach 1.21 (930mph or 1,497km/h) on only its third test flight from Spaceport America, New Mexico.
The milestone, announced on May 26, was reached less than three months after the aircraft’s maiden flight on February 27 and 364 days after the debut of the Mk 1, Hermeus’s earlier, smaller prototype. The two preceding Mk 2.1 sorties were subsonic, focused on validating systems, handling qualities and operational procedures ahead of the high-speed envelope expansion.
The flight took place over the US Army’s White Sands Missile Range airspace. Hermeus has operated out of Spaceport America since December 2025. The Federal Aviation Administration (FAA) has approved Hermeus to conduct up to seven supersonic flights before the end of 2026, indicating that further envelope expansion is expected.
Quarterhorse Mk 2.1 is the first of three planned F-16-scale aircraft in Hermeus’s supersonic development roadmap, with each successive vehicle designed to push performance further toward sustained high-Mach flight.
The aircraft is powered by a Pratt & Whitney (P&W) F100 afterburning turbofan, the same engine used in the F-16 and F-15 fighters. Hermeus says the Mk 2.1 is nearly three times larger and four times heavier than the Mk 1.
AJ Piplica, CEO and co-founder of Hermeus, said, “Our customers at the Department of War are paying close attention to how fast this program is moving. This flight demonstrates a pace of execution that is extremely rare in modern aviation.”
Founded in 2018, Hermeus has built its model around rapid, iterative hardware prototyping, using flight data from each flight to improve performance and reduce risk. The US Air Force awarded the company US$60 million through the AFWERX Strategic Funding Increase (STRATFI) program in 2021 to support the Quarterhorse flight test campaign.
In April 2026 Hermeus closed a US$350 million Series C round, reaching a US$1 billion valuation, and relocated its headquarters from Atlanta to El Segundo, California.
The company is already building and testing Quarterhorse Mk 2.2, with Mk 2.3 to follow. Hermeus is targeting Mach 3 speeds in 2027 and wants to be flying a hypersonic Quarterhorse, the Mk 3 before 2030.
The Mk 3 will be equipped with the company’s Chimera turbine-based combined cycle (TBCC) engine.
On May 28, the company announced a US$159 million contract modification with the Defense Innovation Unit (DIU), taking the total ceiling of its high-Mach flight demonstration contract to US$219 million.
