Castelion closes $1B Series C to scale hypersonic weapons manufacturing

Castelion, a Torrance, California-based defense startup, has closed a $1 billion Series C round, structured as $800 million in equity alongside additional financing, to accelerate production of hypersonic weapons systems for the U.S. military.

The company designs, tests, and manufactures what it describes as affordable hypersonic weapons, vertically integrating core technologies to control cost and speed up development cycles. Its stated approach treats cost and manufacturability as design requirements from day one rather than secondary considerations, with the goal of enabling high-volume production rather than low-rate, bespoke military hardware.

No lead investors were disclosed in connection with the announcement.

Castelion's pitch centers on restoring what it characterizes as America's ability to out-produce strategic rivals through non-nuclear deterrence. The company operates facilities in Torrance and is building out a 1,000-acre site in Rio Rancho, New Mexico, which appears intended to support scaled manufacturing and energetics operations. It also has an engineering presence in Allen, Texas.

Open job postings reflect the breadth of the company's current build-out: roles span flight software, avionics reliability, embedded systems, flight test engineering, automation and controls for hypersonic-flight component production lines, and an energetics safety manager to oversee the handling and storage of propellants and explosive materials at the New Mexico site.

The Series C comes as the U.S. defense establishment has pushed to diversify its supplier base for long-range strike weapons, a category where production capacity has historically lagged stated requirements. Castelion is competing in a segment that has drawn significant government and private investment as hypersonic strike capability becomes a higher Pentagon priority.