Boeing [BA] on April 11 said its venture arm has made an investment in a small British company that is developing hypersonic propulsion technology for aircraft and rockets.

The Boeing HorizonX Ventures investment in Reaction Engines is part of a $37.3 million funding round that includes Britain’s Rolls-Royce and BAE Systems. BAE in 2015 also made an investment in Reaction Engines valued at around $40 million for a 20 percent stake in the company.

The HorizonX investment is also its first in a British company and second in a company involved in engine technology. When Boeing announced the stand-up of HorizonX in April 2017, it disclosed an investment in Zunum Aero, which is a startup that is developing hybrid-electric and electric propulsion systems for passenger planes for regional travel.

Boeing didn’t disclose the amount of its investment in Reaction Engines but said it is in line with the range of other investments by HorizonX, which is from low single millions of dollars to the low double-digit millions of dollars. HorizonX gives Boeing access to cutting edge technologies that could benefit its current and future defense and commercial products.

“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 statement.

Reaction Engines’ key technology effort is its Synergistic Air-Breathing Rocket Engine (SABRE), which is a hybrid of jet and rocket technology capable of reaching Mach 5.4 in air breathing mode and Mach 25 in rocket mode for space flight. Among other things, the company touts its technology as offering low-cost, high-cadence access to space.

The latest funding round was the largest ever for Reaction Technologies and will be used to further develop the SABRE engine, a spokesman for the company told sister publication Defense Daily on April 12. Near-term development milestones include a high temperature heat exchanger test later in 2018 at a company test facility it is building in Colorado to validate the performance of its precooler heat exchanger technology.

The U.S. Defense Advanced Research Projects Agency recently awarded Reaction Technologies a contract to conduct high-temperature airflow testing of the company’s precooler heat exchanger.

The funding will also be used toward ground-based testing of a full SABRE engine core in 2020 at a test facility the company is constructing in the U.K., the spokesman said.

“In addition to providing our largest round of private investment, these new partners bring invaluable expertise in both hypersonics and engine technologies with significant access to target markets,” March Thomas, chief executive of Reaction Engines, said in a statement.

Other investors in the latest funding round include Baillie Gifford Asset Management and Woodford Investment Management, Reaction Engines said.

Reaction Engines has about 150 employees.