Hypersonic aircraft built by iterating one airframe a year
HQ: Atlanta, GA, United States | Founded: 2018 | Employees: Not disclosed in reviewed sources | Stage: Series C; $1B valuation after a $350M round in April 2026; more than $500M raised in total | Website: https://www.hermeus.com
Hermeus was founded in 2018 in Atlanta by AJ Piplica, Glenn Case, Skyler Shuford and Michael Smayda, engineers with backgrounds at SpaceX, Blue Origin and hypersonic programme work. The premise was that the expensive part of hypersonics is not the physics but the programme structure: legacy efforts spend a decade on requirements and a single vehicle. Hermeus instead planned a series of Quarterhorse test aircraft, each slightly more capable, flying roughly one per year. The company now works across Atlanta, Los Angeles, Jacksonville and Washington, D.C.
The company started with propulsion. A 2019 seed engine paired an off-the-shelf PBS Aerospace TJ100 turbojet with a precooler; Chimera I then integrated a GE J85, a precooler, a bypass and a ramjet and demonstrated the turbojet-to-ramjet mode transition at scale. Gryphon I characterised the subscale precooler at high supersonic speeds, and Gryphon II mated the precooler to a 30,000-lbf Pratt & Whitney F100 for ground testing ahead of flight. That lineage leads to Chimera II, the flight-scale combined-cycle engine intended to power Darkhorse. Hermeus raised a roughly $16M Series A in 2020 and a ~$100M Series B in 2022 led by Sam Altman, which funded the first aircraft and ground testing. The Quarterhorse programme produced Mk 0 for ground tests, Mk 1 for subsonic flight, and Mk 2 for supersonic flight, with each vehicle de-risking the next.
Mk 1 flew at Edwards Air Force Base on 27 May 2025. Mk 2.1, roughly the size of an F-16, made its maiden flight at Spaceport America in February 2026, and in April 2026 the FAA issued the clearances needed for supersonic testing. On 26 May 2026 Mk 2.1 flew supersonically for the first time, reaching Mach 1.21 — a modest number by hypersonic standards but a large milestone for a startup that had never flown faster than sound, and one the company says made it the fastest in aviation history from founding to supersonic flight, 364 days after its first flight. The company frames the cadence itself as the achievement: one aircraft per year, each one teaching the next, with the next Mission Plane and then Darkhorse (targeted for 2030) carrying the programme toward operational high-Mach flight.
The customer base is the U.S. military. The Defense Innovation Unit has funded Hermeus since the Darkhorse concept, and in May 2026 a $159M modification took the total ceiling to $219M, covering high-Mach flight tests and high-speed payload release with the Air Force and Navy through 2027. Hermeus is also developing Darkhorse, a reusable uncrewed hypersonic aircraft intended for defense missions and targeted for 2030, and Halcyon, a Mach 5 passenger concept that remains a long-horizon ambition. In April 2026 the company raised a $350M Series C at a $1B valuation, split between $200M of equity led by Khosla Ventures and $150M of debt, bringing total funding above $500M. Zach Shore, previously President and Chief Revenue Officer, became CEO; co-founder AJ Piplica moved to Executive Chairman.
Hypersonics has historically been a government programme measured in decades and billions. Hermeus is trying to run it like a hardware startup: build a Quarterhorse airframe each year, fly it, learn, and build the next one. That cadence is the strategy, and in 2025-2026 it started producing evidence — Mk 1 flew in May 2025, Mk 2.1 flew in February 2026, and on 26 May 2026 it became the company's first aircraft to fly supersonically, reaching Mach 1.21. The FAA cleared it for supersonic flight in April 2026, which matters because it lets Hermeus test in U.S. airspace rather than depending on a handful of corridors or ranges.
Money followed the flights. In April 2026 Hermeus closed a $350M Series C — $200M of equity and $150M of debt, led by Khosla Ventures — at a $1B valuation, taking total capital raised above $500M. A month later the Defense Innovation Unit expanded its agreement by $159M to a $219M ceiling, one of the largest DIU awards on record, covering high-Mach flight tests and high-speed payload release with the Air Force and Navy through 2027. That combination — private capital plus a defense customer paying for demonstrations — is the right structure for a company whose product is still a prototype.
What it has not done is prove the hardest part: a turbine-based combined cycle engine that can take off from a runway, accelerate through the transonic regime and sustain hypersonic flight. Its Chimera engine programme is the technical core and the biggest single risk. The roadmap runs Quarterhorse (uncrewed testbed) to Darkhorse (reusable military aircraft) to Halcyon (a Mach 5 passenger concept), and each step needs the previous one's engine, thermal management and flight controls to work. If Hermeus can keep its annual flight cadence and turn Darkhorse into a program of record, it becomes one of the few credible Western hypersonic primes outside the legacy contractors. If the engine or the funding cycle slips, the $1B valuation is a bet on a demonstrator.
Category: Aerospace & Defense Startups
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