Boeing’s HorizonX venture investment arm is placing a big bet on hypersonic flight.

Today it announced that it’s going in with Rolls-Royce and BAE Systems on a $37.3 million Series B investment round for Reaction Engines, a British aerospace startup focusing on a hybrid rocket-jet propulsion technology that could send aircraft zipping into space and back at multiple times the speed of sound.

“As Reaction Engines unlocks advanced propulsion that could change the future of air and space travel, we expect to leverage their revolutionary technology to support Boeing’s pursuit of hypersonic flight,” Steve Nordlund, vice president of Boeing HorizonX, said in a news release.

Boeing has long been working on hypersonic technology: The Boeing-built Air Force X-51 Waverider scramjet-powered vehicle set a world record for air-breathing hypersonic flight in 2013, and just a couple of months ago, Boeing unveiled its latest concept for a hypersonic demonstrator airplane.

Reaction Engines was founded in 1989 with the aim of pursuing new approaches to high-speed point-to-point travel. Its propulsion system is known as the Synergetic Air-Breathing Rocket Engine, or SABRE. The SABRE engine is theoretically capable of Mach 5 travel in air-breathing mode and Mach 25 travel in rocket mode for spaceflight.

One of the system’s innovations is an ultra-lightweight heat exchanger that keeps engine components from overheating at high speeds. Last September, Reaction Engines’ U.S. subsidiary won a contract from the Pentagon’s Defense Advanced Research Projects Agency, or DARPA, to validate the heat exchanger for Mach 5 flight.

Reaction Engines is aiming to conduct ground testing of the SABRE engine core by 2020. The company has also talked about developing a hypersonic space plane called Skylon that could begin uncrewed flight tests as early as 2025.

The company’s CEO, Mark Thomas, said he was “thrilled and honored” to be chosen as Boeing HorizonX’s first investment in a British company.

“Boeing is a world leader in many fields, bringing invaluable expertise in hypersonic research and space systems. … This is a very exciting step that will contribute to our efforts to develop a commercial technology business and accelerate opportunities to further the future of air and space travel through SABRE technology,” he said.

Reaction Engines already has well more than 100 employees. Past investment rounds have provided more than $100 million, with the British government and BAE Systems among leading backers.

HorizonX was created a year ago to serve as Boeing’s channel for outside investments in technologies that are relevant to the company’s interests in aerospace, manufacturing and communication. This is the second HorizonX investment in a company headquartered outside the U.S.

Boeing doesn’t disclose the size of its HorizonX investments, other than to say that they typically range from seven figures to the low eight figures.

Other companies in the HorizonX Ventures portfolio include:

Myriota , an Australian venture focusing on satellite communication services for Internet of Things devices.

, an Australian venture focusing on satellite communication services for Internet of Things devices. Fortem Technologies for drone radar navigation systems.

for drone radar navigation systems. Cuberg for advanced batteries.

for advanced batteries. Gamma Alloys , for next-generation aluminum alloys.

, for next-generation aluminum alloys. Near Earth Autonomy for autonomous flight control systems.

for autonomous flight control systems. C360 for augmented reality and virtual reality used in immersive videos.

for augmented reality and virtual reality used in immersive videos. Upskill for augmented-reality solutions for industrial settings.

for augmented-reality solutions for industrial settings. SparkCognition for AI tools used with the Internet of Things.

for AI tools used with the Internet of Things. Zunum Aero for hybrid-electric airplane propulsion.

Update for 7:08 p.m. PT April 11: The British government passed along this statement about the Reaction Engines deal from Sam Gyimah, minister of state for universities, science, research and innovation: