In this particular case, the V-22 Osprey is a multi-purpose aircraft with two large pivoting helicopter rotors for engines. These rotors allow the aircraft to take off and land like a helicopter but fly like a standard airplane. The USMC and Air Force use this craft for both combat and rescue missions. The craft has a mixed reputation due to its increased budgetary footprint and controversial safety record. The development budget for the Osprey program was originally $2.7 Billion in 1986, but it has risen to a total of $27 billion expended on the program in total as of 2008. Another $27 billion is projected as necessary for reaching target production levels by the end of the program. There has been criticism that a helicopter with equivalent performance could be produced for much less than this. In terms of safety, the Osprey has claimed the lives of 30 people during testing, and there are concerns that the Osprey may not always be capable of making emergency landings.
With the deadline looming for the supercomittee to cut the budget, programs like this would normally be given the axe. However, due to a concerted lobbying effort by the USMC and congressmen such as William M. Thornberry (R-Texas), whose districts are involved in the aircraft's manufacture, not even Dick Cheney was able to kill the program, only potentially scale it back.
As long as there are entrenched interests involved in the procurement process, particularly with congressional districts, the military is going to have extreme difficulty cutting obsolete or prohibitively expensive programs (like the Osprey or F-35 JSF). And considering the budgetary climate, DoD is going to need to make meaningful cuts if we're going to even get a handle on the debt.