The U.S. Air Force's Northrop Grumman B-2 Spirit Bomber, introduced into service in 1997, remains today the most expensive combat aircraft ever to enter service in the world. The platform's numbers were cut significantly due to significant cost overruns, underperformance, and a contraction of military spending following the end of the Cold War. Only 21 bombers entered service, costing well over $2 billion each when including research and development costs. The bombers' performance had several shortcomings, including extreme maintenance requirements and extreme fragility when exposed to the elements. All bombers had to be stored in specially built air conditioned hangers to protect against the weather, while they were known to be extremely vulnerable to rain. In February 2008 a B-2 Spirit crashed at Andersen Air Force Base, Guam. While both crewmen ejected successfully, the loss amounted to billions of dollars and the bomber was damaged beyond repair. All 20 remaining B-2 platforms were subsequently grounded for two months while an investigation into the causes of the crash was undertaken. The investigation concluded that the cause of the crash was 'heavy lashing rains' which had damaged the bomber while it had been outdoors. Moisture had entered the bomber's skin flush air data sensors - data from which was used to calculate numerous critical factors including airspeed and altitude. With the sensors compromised, the flight control computers had calculated an inaccurate angle of attack and airspeed, and as a result the bomber rotated twelve knots slower than intended. The result was that upon takeoff, the bomber began an uncommanded 1.6g 30 degree pitch up manoeuvre which led to a crash. The left wing tipped and gouged the runway, and the aircraft hit the ground and burned. The crash was the most expensive in U.S. military history, and represented a loss of 4.8% of the Air Force's B-2 fleet. Two years later in 2010 a second B-2 accident occurred at Andersen Air Force Base, and the bomber was severely damaged by a fire on the ground. This second incident did less damage to the platform, which was returned to service after almost two years of repairs. The U.S. Air Force today plans to retire its B-2 fleet several decades before originally planned, in part due to the platform's&nbsp;delicacy and extreme maintenance requirements. The fleet is set to be replaced by the B-21, a stealth bomber which will be fielded in similar numbers to those originally intended for the B-2. While its usefulness was limited and it never saw combat against advanced enemy air defences, against which it was built to engage, the B-2 acted as an effective technology demonstrator from which the military learned a great deal. The new B-21 stealth bomber is set to improve on several of the B-2's shortcomings, and is likely to have lower maintenance requirements and higher durability. Ultimately the 2008 crash at Andersen Air Force base serves as a reminder of the vulnerability and delicacy of the B-2 platform even in peacetime, and its infeasibility in a major war when facilities critical to maintaining it and protecting it from weather are highly likely to come under attack. The crash of 2008 demonstrates the extreme delicacy of the B-2 the Air Force's need to replace the platform with the B-21 in the near future to maintain a viable modern bomber - particularly in light of Russia and China both developing their own next generation strategic bombers.