Boeing's HorizonX venture fund has invested in UK-based specialist in hypersonic propulsion company Reaction Engines.

Boeing says that the company is known for its Synergistic Air-Breathing Rocket Engine (SABRE), which blends both jet and rocket technology. This will allow speeds of Mach 5 in air-breathing mode and Mach 25 in space flight mode.

The investment was part of a $37.3 million Series B funding round that also involved Rolls-Royce and BAE Systems. Boeing did not disclose the amount it invested.

"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," said Steve Nordlund, vice president of Boeing HorizonX.

"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," says Reaction Engines chief executive Mark Thomas.

In April 2017, Boeing announced the creation of the HorizonX business unit and venture capital fund.

The HorizonX portfolio is intended to increase Boeing's involvement in emergent technologies in aerospace and manufacturing, such as autonomy, energy storage, advanced materials, augmented reality, software, machine learning, propulsion, and the 'Internet of Things'.