The US Air Force is unlikely to purchase initial hypersonic weapons in large quantities, but instead will wait for improvements in follow-on versions.

The service expects an initial operational capability of 2020 for its Hypersonic Conventional Strike Weapon (HCSW), though there may be some delays due to testing, said Will Roper, USAF assistant secretary for acquisition and technology.

The USAF also believes it has an easier path to field a hypersonic weapon compared to the US Navy or Army, especially because of the service’s large testing and launch platform, the Boeing B-52 Stratofortress, he says.

“The B-52 is very forgiving about what it carries,” says Roper. “We do have to worry about cold temperatures, but we don’t have to shrink down the volume.”

In April, the USAF announced a $928 million award for Lockheed Missiles and Space to develop the HCSW, an air-breathing, ram-jet-powered cruise missile.

It awarded a separate $780 million contract to Lockheed Missiles and Fire Control in 2017 to develop the Air-launched Rapid Response Weapon (ARRW), a boost glide hypersonic system, which uses a rocket to accelerate its payload to high speeds, before the payload separates from the rocket and glides unpowered to its destination at hypersonic speeds up to Mach 20.

The initial versions of HCSW probably will be purchased in limited quantities, pending improvements to follow-on weapons, says Roper.

“A lot will depend on what comes out of the programme,” he says. “I expect this will be a classic spiral development programme where you’ll go into some low rate of production, keep spiraling the technology until you get enough bells and whistles on the weapon, and you say, ‘That’s the one I want to buy .’”