The U.S. Air Force’s new B-21 stealth bomber could fly as early as December 2021, Air Force vice chief of staff Gen. Stephen Wilson said at an event in Washington, D.C. on July 24, 2019.

Air Force magazine broke the news.

Wilson told the audience he in recent weeks visited Northrop Grumman’s facilities in Melbourne, Florida, where he was “looking at the B-21.” Northrop is “moving out on that pretty fast.” Wilson said, adding he has an app on his phone “counting down the days … and don’t hold me to it, but it’s something like 863 days to first flight.”

“That would put the first flight of the B-21 in December 2021,” Air Force editor John Tirpack noted. “The Air Force has said from the beginning that the first B-21 would be a ‘useable asset’ but has also said it doesn’t expect an initial operating capability with the B-21 before the ‘mid-2020s.’”

The Air Force still is mulling how many B-21s to buy. “We’re exploring the force structure between the B-1, the B-2 and the B-52,” Wilson said.

Wilson stressed that the service needs “at least 100” B-21s.

The Air Force repeatedly has said that, in the 2030s, it will retire its 62 1980s-vintage B-1 bombers and, a few years later, also will retire all 20 '90s-vintage B-2 stealth bombers.

Meanwhile, the service would upgrade 76 B-52s that first flew in the early 1960s and buy at least 100 new B-21 stealth bombers. The result in the 2040s would be a force of around 175 bombers composed of factory-fresh B-21s and 80-year-old B-52s.

"That plan has not changed," Heather Wilson, the former service secretary, said in February 2019. "We need a minimum of 175 bombers, is what we announced last year,” Wilson added, "and that they will be a mix of B-21s and B-52s."

But Heather Wilson's announcement raises a multi-billion-dollar question. How does the Air Force plan to equip the five new bomber squadrons the service said it needed as part of its September 2018 plan to grow from 312 squadrons to 386?

Since the Air Force announced that plan, it has shuttered one F-22 squadron and redistributed the unit's planes, meaning that in early 2019 the service had just 311 squadrons. It would need to add 75 new units to meet the expansion goal.

Those units could require hundreds of new aircraft costing hundreds of billions of dollars.

In early 2019 the Air Force maintained nine front-line bomber squadrons at bases in Missouri, Texas and North and South Dakota. A bomber squadron typically has eight aircraft. The balance of the bomber fleet belongs to training units or is undergoing deep maintenance.

Adding five new squadrons could compel the Air Force to acquire around 75 extra bombers in addition to the 100 it committed to buying when, in 2015, it awarded Northrop Grumman the B-21 development contract.

The flying branch expected a single new B-21 to cost around $600 million. It could set back U.S. taxpayers $45 billion to equip the extra bomber units with new planes.

For now, the Air Force holds competing positions. One, that an expansion of the bomber force is necessary. And two, that it will maintain an inventory of 175 bombers, just enough for the current force structure. It’s unclear how the service will reconcile the two positions.

“The general consensus is, we don’t have enough long-range strike capacity,” Stephen Wilson said.

So why not just keep B-1s and B-2s flying for longer? As recently as 2016, the Air Force estimated the B-2s could continue operating into the 2060s. The swing-wing B-1s are mechanically unreliable and suffered heavy wear and tear during the air campaigns over Iraq and Afghanistan. The Air Force in 2016 assumed the B-1s would retire in the 2040s.

The Air Force is spending billions of dollars upgrading the B-52s with new engines, electronics and weapons. Similar upgrades, in theory, could extend the useful lives of five squadrons' worth of B-1s and B-2s at lower cost than 75 new B-21s.

The Virginia-based Mitchell Institute for Aerospace Studies endorsed bomber upgrades. "The good news is that a pathway exists for the Air Force to grow its bomber force," institute experts David Deptula and Douglas Birkey wrote. "This will require retaining and modernizing the B-1B, B-2 and B-52, with B-21s procured additively."

David Axe serves as Defense Editor of the National Interest. He is the author of the graphic novels  War Fix, War Is Boring and Machete Squad.