Northrop Grumman has finished preliminary design review of the B-21 Raider stealth bomber.

The heavy bomber is now moving towards a critical design review, says Lt Gen Arnold Bunch, the air force's military deputy for acquisition during an 18 April Senate Armed Services hearing. Critical design review is the next step before assembly of the first aircraft can begin.

Northrop Grumman has also delivered the first set of software for the B-21 programme, said Bunch.

“We are making good progress,” he said. “I am comfortable today with were we are at, the progress that Northrop Grumman is making on the programme.”

The USAF has released little detail on the schedule for the B-21’s development and delivery, but said the aircraft will be fielded in the mid-2020s. The service plans to buy 100 B-21s, enough to retire by 2040 its fleet of 20 Northrop B-2 Spirit stealth bombers and 62 Boeing B-1B Lancer bombers.

Citing military secrets Bunch declined to say much more about the B-21 programme. However, his USAF colleague, Lt Gen Jerry Harris, deputy chief of staff for strategic plans and requirements, appeared to indicate that the service may ask for funding to acquire dozens of additional B-21 Raiders.

“We would like to fix the nine squadrons (of bombers) we have right now to give them more airplanes per squadron and then continue to grow to somewhere in the neighborhood of 14 or 16 squadrons that are ready for the mission,” he said.

Because the B-21 Raider is the only bomber in development at this time it would likely be a leading candidate to fulfill that vision of a larger bomber force.