The US Air Force has confirmed plans to re-engine the Boeing B-52H fleet and retire the Northrop Grumman B-2 and the Rockwell B-1 as Northrop’s next-generation B-21 stealth bomber ramps up deliveries.

The proposals in the Trump Administration’s Fiscal 2019 budget request will consolidate the Air Force’s strategic bomber fleet to the B-21 and a re-engined B-52 fleet after around 2040.

The Air Force has not released details of the schedule for the B-21’s development, initial operational capability and deliveries, but says only the secretive new stealth bomber will be fielded in the mid-2020s.

The service’s plans to buy 80-100 B-21s roughly correlate to the existing fleet of 20 B-2s and 62 B-1s.

“If the force structure we have proposed is supported by the Congress, bases that have bombers now will have bombers in the future,” says secretary of the Air Force Heather Wilson. “They will be B-52s and B-21s.”

The current B-52H fleet became operational in 1961, nine years after the original B-52A entered service. The Air Force’s plans to replace the fleet in the 1960s with the Mach 3 North American B-70 Valkyrie died when the latter was cancelled. The B-2s cost overruns and budget cutbacks in the early 1990s doomed plans to shepherd Boeing’s 1950’s-era bomber out of service.

Although it mainly operations as a conventional bomber in undefended airspace today, the B-52H still has the capability to launch long-range cruise missiles with nuclear warheads.

The Air Force plans to replace the eight Pratt & Whitney TF-33s on each bomber with a new engine. In December, the Air Force released details of the replacement strategy. Instead of consolidating B-52’s engine-count from eight to four, the Air Force plans to minimise design changes by keeping the same number.

That strategy narrows the likely options for the Air Force to three engines: GE Aviation’s Passport, Pratt & Whitney Canada’s PW800 and Rolls-Royce’s BR.725.

The initial operational capability for the re-engined B-52H is scheduled in 2029 under the most likely budget scenario.