“Taken together – 120 combat-coded bombers, 20 trainers, and 24 planes for backup and attrition planning purposes – the minimum buy would be 164 aircraft."

Northrop Grumman’s B-21 Raider stealth bomber is rapidly approaching its critical design review (CDR), when a Pentagon review team will determine if the new aircraft is meeting the technical requirements set forth in its requirements documents.

If the design passes its CDR, the B-21 team will be cleared to build, integrate and test the aircraft before its next hurdle: the production readiness review. The idea is to ensure that the B-21 will meet its stated performance requirements within cost, schedule and risk tolerances.

“We haven’t done CDR yet, we are on our way to critical design review,” Randy Walden, director and program executive officer for the Air Force Rapid Capabilities Office—which is responsible for B-21 program—said during an speaking engagement held at the Air Force Association’ Mitchell Institute on June 25.

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“I suspect it will be done before the end of the year. That's our plan today.”

Once the B-21 completes its CDR, the aircraft will be well on its way towards flight-testing and production. The Air Force has already conducted wind tunnel testing of the new bomber and it has also done component level testing, but until the aircraft actually makes its first flight there are many unknowns.

However, the first step is to have a finalized design ready.

“From my perspective, this is about producing 100 bombers, not about just getting through development,” Walden said.

“Development is a phase that leads into the fielding of this critical need. So my focus is getting the production started, but I can’t do that until we understand what the design looks like.”

Unlike most other major defense programs, the B-21 is not only being developed mostly in secret, it is also being managed outside the normal acquisition process at the Air Force’s Rapid Capabilities Office. The reason for that is fairly simple, the Air Force hopes that the secrecy will prevent adversaries such as Russia and China from gaining too much insight into the new bomber and its capabilities before it is even fielded.

“There are adversaries out there that want to know what we’re doing, and are probably going to great lengths to try to get to that level of insight,” Walden said.

“We’re doing everything we can to prevent that.”

However, while the Air Force is doing everything it can to prevent Moscow and Beijing from gaining intelligence on the B-21 and its capabilities, the service may not have fully considered emerging Russian and Chinese long-range precision-guided strike capabilities when it set the requirement to build only 100 Raiders.

Indeed, even as the Raiders come online, the Air Force intends to retire its fleet of 62 supersonic Rockwell International B-1B Lancers and 20 stealthy Northrop Grumman B-2A Spirit bombers. That would leave 76 Boeing B-52s—which are likely to be re-engined—along with 100 B-21s to make up the Air Force strategic bomber fleet in the years beyond the 2030s.

Given that in both the European and the emerging Indo-Pacific theatres, both Russia and China possess long-range precision-guided weapons that could target and knock out airfields and other critical infrastructure in the region, the Air Force might find that short-range tactical aircraft are not going to be able to operate freely in the coming decades.

That problem is further compounded if Russia and China use their long-range combat aircraft in combination with new extremely long-range air-to-air missiles to target American aerial refueling tankers, command and control assets as well as intelligence, surveillance and reconnaissance aircraft to cut the sinews of allied air operations over Europe or the Western Pacific. In that case, the Air Force would likely need far more than 100 B-21 Raiders to deliver strikes against the enemy.

The Air Force does not necessarily disagree with that assessment. Testifying before the House Armed Services Committee on May 25, 2017, Lt. Gen. Arnold W. Bunch Jr., military deputy, Office of the Assistant Secretary of the Air Force for Acquisition, said that 100 B-21 bombers is the floor of the Air Force requirement.

“It’s not just a hundred to go do missions,” Bunch told the House Armed Services Committee.

“It’s at least a hundred to do all the training, to do the depot maintenance.”

The Air Force flag officers testifying before the Congress also agreed that the service might need as many as 258 B-21 bombers in the nightmare scenario of a war with the Russian Federation.

“Those numbers aren’t incorrect,” Lt. Gen. Jerry D. Harris, Air Force deputy chief of staff for strategic plans and requirements, told the Congress. “We do agree that probably 165 bombers is what we need to have.”

But the Air Force senior leadership quickly walked back Bunch and Harris’ testimony. In the days following Bunch and Harris’ testimony, Air Force secretary Heather Wilson and the service’s chief of staff Gen. David Goldfein would say only that the Air Force needs 165 bombers in total.

Nonetheless, other studies—such as one conducted by the Center for a New American Security (CNAS)—have also shown that the Air Force needs at least that many B-21s.

“When considering theoretical requirements of up to 200-plus bombers to prosecute a penetrating strike mission against a great power such as Russia or China, it is better to err on the side of caution and maintain a healthy complement (24) of backup and attrition aircraft,” report authors Jerry Hendrix, CNAS’ then director of defense studies and Air Force Lt. Col. James Price wrote .

“Taken together – 120 combat-coded bombers, 20 trainers, and 24 planes for backup and attrition planning purposes – the minimum buy would be 164 aircraft.”

Based on the need to fill out 10 squadrons of 12 aircraft each for 10 Air Expeditionary Force wings, the Air Force would need a total of 120 combat-coded B-21 bombers.

“While each AEF comprises an assortment of tactical, strategic, and logistical aircraft, the current Air Force force structure is unable to meet the requirement to supply each AEF with one bomber squadron made up of a minimum of 10 and optimally 12 bombers,” the authors wrote.

Shuffling aircraft around in order to meet immediate operational needs would be detrimental for both maintenance and aircrew training.

“Should one deploying squadron rob another of its aircraft to meet requirements, the robbed aircraft will not be available for scheduled maintenance and training evolutions of the home-based AEF. Such conditions also create the accelerated demise of the force as the smaller numbers of aircraft are used at ever-increasing rates,” the authors wrote.

“Therefore, it is important to establish a baseline of 12 combat-coded bombers per squadron, and 10 squadrons to fill out the 10 AEFs, resulting in a minimum requirement of 120 combat-coded bombers.”

But even 120 combat-coded bombers would get the United States part way to a force that could conduct a full-scale air war against the Russian Federation.

“An air campaign against Russia is projected to last 180 days at a minimum and would require nearly 260 bombers,” the authors wrote.

“Today the Air Force has fewer than 100 combat-coded bombers, well shy of the levels required to respond to two regional conflicts simultaneously.”

The bottom line is that the Air Force needs many more B-21s than the 100 it is currently planning to buy. Not building more is essentially a waste of the Pentagon’s research and development funds and a waste of the nation’s investment in the production tooling and workforce.

Dave Majumdar is the defense editor for the National Interest. You can follow him on Twitter: @davemajumdar.