WASHINGTON — Castelion, a defense technology startup led by former SpaceX engineers, announced Dec. 5 it raised $350 million in Series B financing to accelerate high-volume production of hypersonic weapons for the Pentagon.
The California-based company has positioned itself as a vertically integrated builder of hypersonic missiles, an area where U.S. officials acknowledge a lag behind China and Russia. Castelion’s first weapon is being developed for the U.S. Army and Navy, and the firm has secured multiple research and development contracts from the Air Force Research Laboratory.
The latest financing was led by Altimeter Capital and Lightspeed Venture Partners, with participation from Lavrock Ventures, Andreessen Horowitz, General Catalyst, First In, Space VC, Cantos, BlueYard, Avenir, Champion Hill and Interlagos. The backing reflects a widening investor appetite for hardware-centric defense startups that promise rapid design cycles and commercial-style production methods.
Castelion is seeking to “close America’s hypersonic capability gap against China and Russia,” said Bryon Hargis, CEO and co-founder. “This funding lets us build fast, test often, and produce at volumes that matter in the real world.”
The company last month unveiled plans for a 1,000-acre campus in New Mexico dedicated to next-generation hypersonic systems. The site is expected to support solid rocket motor production, static testing and final assembly of completed rounds.
Investors say the company’s rapid pace has been central to its appeal. Erik Kriessmann, partner at Altimeter Capital, said Castelion was “founded by a special team of SpaceX alumni who, in just 2.5 years, took a clean-sheet hypersonic from concept to 25+ flight tests and major integration contracts.”
Alex Poulin, partner at Lavrock Ventures, added that “hypersonics only matter if you can build them at scale. Castelion’s team understands that … we’re proud to be early backers of a team focused on delivering capacity, not just concepts.”
The Series B raise follows a steady funding climb. In January 2025, Castelion reported a $100 million infusion that included $70 million in Series A capital led by Lightspeed and $30 million in venture debt from Silicon Valley Bank. That came after a $14.2 million seed round.
