Although the B-2 Spirit stealth bomber is one of the newest aircraft in the US Air Force's arsenal, its maintenance and operational needs have caused the USAF to request authorization for several different modernization projects in the coming fiscal year.
With only 20 of the stealth aircraft in service, the mission-capable rate of the B-2 is lower than most other aircraft. It did rise to 56.9% in fiscal-year 2014, however, up from 46.7% in fiscal-year 2013. This increase came about primarily from a cost-effective program to maintain one of the highest-maintenance areas of stealth aircraft - the stealth materials on the aircraft's skin - according to the Assistant Secretary of the Air Force (Acquisition) William LaPlante. The B-2s are also continuously cycled through the maintenance depot, to prevent excessive wear on any single airframe. The depot maintenance takes around 13 months to complete for a single aircraft.
Some of the requested modernization projects include upgrade the B-2's Defensive Management System (DMS), which uses on-board computers and antennas to inform and alert the crew of various threats and their detection capabilities. Other upgrades include the ability to carry more advanced weaponry, such as the B61-12 (a 50-kiloton nuclear bomb fitted with a tail kit to give it JDAM-like accuracy) and the Long Range Standoff Weapon, essentially a cruise missile with the option to use a nuclear warhead.