The U.S. Military is currently the world's largest operator of strategic bombers, and alongside Russia, China and North Korea is one of only four armed services in the world to retain such platforms in service. The U.S. Air Force's fleet currently consists of three bomber variants, the Vietnam War era B-52 Stratofortress dating back to 1955, the late Cold War era B-1B Lancer dating back to 1986, and the stealthy B-2 Spirit in service since 1997. The latter two today represent the most recent bomber designs to be developed in anywhere in the world, while the B-52 is among the oldest aircraft in service in the U.S. military. It therefore came with some surprise to a number of analysts when the U.S. Air Force established plans to retire both the B-1B and B-2 from service by the mid 2030s while retaining the B-52 in service indefinitely. This decision was testament to the value of the B-52's older and in many ways more reliable technology over its state of the art alternatives.
The reasons for the U.S. Air Force's decision are manyfold, and pertain to both the different role and many advantages of the B-52 over newer platforms. While the B-52 as first fielded in the Vietnam would fare poorly on a modern battlefield, the platform has been extensively upgraded to give it capabilities far surpassing those it originally fielded. Of particular note, the somewhat cumbersome aircraft which would today be extremely vulnerable to enemy air to air and surface to air missiles has been thus modified to allow it to strike from a long range using both ballistic and cruise missiles rather than relying on conventional bombs. New engines, avionics, fire control systems and other systems have also extensively enhanced the B-52's capabilities. The bomber today, well over 60 years since it entered service, is prized over its more modern counterparts for its far lower maintenance requirements and higher sortie rate, which combined with its high payload allow it to deploy massive firepower at a rate the B-1B and B-2 cannot match. The platform's simplicity over the swept wing B-1B and extremely delicate B-2 gives it a significant advantage.
With the U.S. Air Force expects to induct its first B-21 bombers, a highly secretive stealth platform which improves on several of the critical performance flaws found on the B-2, in the near future. The new bomber is expected to replace both the B-2 and B-1B in service. While it will have lower maintenance requirements than the B-2 it will still be unable to fulfil the role of the B-52, and it is for this reason that the U.S. bomber fleet will in future rely on a pairing of the B-21 and B-52 - two bombers inducted into service over seventy years apart. While the B-2, a relatively recent addition to the fleet and by far the world's most modern bomber, was expected to remain in service into the second half of the century, its many performance failures have made operating the platform highly impractical and extremely costly even by the standards of the U.S. Air Force. It will be retired alongside the B-1B by the mid 2030s, likely before their replacement the B-21 full enters service. The B-21 is set to built on several of the technologies pioneered by the B-2, and will represent a new generation of bombers to contend with China's Xian H-20 and Russia's PAK-DA - both currently under development. Ultimately the B-52's continued service is a testament to the value of older and simpler technologies over more modern, high maintenance and complex alternatives - and shows that early Cold War era platforms can retain significant value in combat today if properly modernised. Having entered service just two years after the Korean War, and predating even the Vietnam War's MiG-21 and F-4 fighters, the B-52 could well see service with the U.S. Air Force into the second half of the 21st century.