Castelion, a defense tech company established by former SpaceX engineers, announced on December 5th that it has secured $350 million in Series B funding. The aim is to ramp up the production of hypersonic weapons for the Pentagon.
Based in California, Castelion is working towards becoming a vertically integrated manufacturer of hypersonic missiles. This is an area where U.S. officials have acknowledged a deficit compared to China and Russia. The company's initial weapon is being developed for both the U.S. Army and the Navy, and they have also received several research and development contracts from the Air Force Research Laboratory.
The latest round of funding was spearheaded by Altimeter Capital and Lightspeed Venture Partners, with contributions from Lavrock Ventures, Andreessen Horowitz, General Catalyst, First In, Space VC, Cantos, BlueYard, Avenir, Champion Hill, and Interlagos. This investment demonstrates growing investor confidence in hardware-focused defense startups promising quick design processes and commercial-style production approaches.
Bryon Hargis, CEO and co-founder of Castelion, stated that they are aiming to “close America’s hypersonic capability gap against China and Russia.” He added, “This funding lets us build fast, test often, and produce at volumes that matter in the real world.”
Last month, the company revealed plans for a 1,000-acre campus in New Mexico dedicated to advanced hypersonic systems. This site will handle solid rocket motor production, static testing, and final assembly.
According to investors, the company's speed is a major factor in its appeal. Erik Kriessmann, partner at Altimeter Capital, noted that 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, emphasized the importance of scalability, stating 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 funding follows previous investments, including a $100 million infusion in January 2025, comprised of $70 million in Series A capital led by Lightspeed and $30 million in venture debt from Silicon Valley Bank. This followed an initial $14.2 million seed round.