Air Force leaders have not backed off their push to retire the A-10 in the Pentagon's fiscal 2016 budget request while the service has significantly boosted its investment in developing a next generation bomber, according to service budget documents.

The Air Force is requesting about $137.8 billion in its fiscal 2016 proposed budget as part of the overall $585 billion the Pentagon has requested for 2016. The $137.8 billion represents a slight budget reduction from the $138.3 the Air Force received in 2015.

Air Force leaders have said the budget has forced the service to balance maintaining the aging fleet while also paying for the development of next generation aircraft like the Long Range Strike Bomber.

Congress has flatly denied the Air Force's previous attempts to retire the A-10 fleet that Air Force leaders have said is necessary in order to free up funding and manning for the introduction of the F-35A.

The A-10 is a popular close-air-support, ground attack aircraft that has received support from prominent lawmakers to include Sen. John McCain, R-Arizona, chairman of the Senate Armed Services Committee.  Notably, the A-10 is flying combat missions in Iraq against Islamic State in Iraq and Syria (ISIS) forces.

Although the Air Force has maintained course on the A-10, service leaders have listened to lawmakers' rejection of its proposal to retire the U-2 Dragon Lady spy plane. The service will push back the proposed retirement to 2019 and has instead requested funding for upgrades to the aircraft.

The Air Force had planned to retire the U-2 in favor of the unmanned Global Hawk system. At the time, Defense Secretary Chuck Hagel said the decision was a  "a close call," but that reduced Global Hawk operating costs, its greater range and endurance made it the "better high-altitude reconnaissance platform for the future."

Supporters for the U-2 have said the Global Hawk is not ready to take over for the Dragon Lady's spy mission. The proposed budget includes funding for the U-2 and the Global Hawk Block 30 and 40 drones.

The Air Force is seeking $1.24 billion for research and development of its long-range strike bomber, or about $300 million over what it funding for the current year. Funding will dramatically increase in coming the coming years.

Air Force generals plan to request $2.2 billion in fiscal 2017, $2.8 billion in 2018, $3.6 billion in 2019 and $3.7 billion in 2020. Air Force Chief of Staff Gen. Mark Welsh has called the Long Range Strike Bomber one of the Air Force's top priorities.

The service plans to continue to buy more F-35A Joint Strike Fighters. The Air Force requested about $600 million to buy 44 more of the fifth generation fighters.

Additionally, the Air Force requested funding to buy 29 MQ-9 Reaper unmanned systems at a time when the service is still working to catch up with demand for the drone.

An aircraft fleet that will be taking a hit in 2016 is F-15C/D. Ten will be retired from the fleet in 2016, according to budget documents.

-- Bryant Jordan can be reached at bryant.jordan@military.com

-- Michael Hoffman can be reached at mike.hoffman@military.com