A rendering of the upcoming B-21 stealth bomber Northrop Grumman

The B-21 Raider, the US Air Force's (USAF) next gen stealth bomber, will soon phase out the B-2 Spirit and the B-1B Lancer. The first batch of B-21s are expected to be fielded within the next decade.

Plans to begin mothballing – retire equipment, but keep them in working condition – the USAF's main two bombers will be officially submitted as part of the 2019 White House budget request, reports Popular Mechanics. While this is part of the request, the decision ultimately comes down to congressional approval.

USAF reportedly plans to eventually purchase and operate a fleet of 100 B-21 Raiders which is going to cost them $80bn. This price tag includes both the jets as well as the support equipment. The secretive B-21 programme is yet to even release images of the bomber. Only concept art of what the jets will look like have so far been released by Northrop Grumman - the designers and builders of the aircraft.

From renders, the B-21 resembles the B-2's wedge-like design and suggests that the B-21 will be an overhaul and update of the B-2, notes the report. What is known about this project, however, is that it will feature the latest in stealth technology and be able to penetrate deep into enemy territory. A USAF statement about the B-21 did mention that its design, "allows for the use of mature systems and existing technology," notes the report. There are also reports that suggest the B-21 will have a drone mode as well.

Funds that go into the upkeep of the B-2 and B-1B can be diverted into the B-21 Raider and this is what the USAF is going for. However, the Air Force has no plans to retire its longest serving bomber- the B-52. In fact, the plan is to replace the ageing engines in the B-52 and keep the heavy bomber relevant for a few more generations.

The B-52 is a workhorse that can carry nuclear bombs, cruise missiles, and there are plans to equip them with the latest generation of the Long Range StandOff (LRSO) stealthy nuclear tipped cruise missile, reports Popular Mechanics.

Reports emerged last year that USAF was testing the B-21 at Area 51 and that new runways were being built specifically for this.