One of the major problems with buying expensive military equipment is the manufacturers promises of how long the item, particularly aircraft, will last. A case in point is the most widely used aircraft in American service. Buyers were told that the aircraft was good for at least 8,000 hours of use. But the F-16 proved to be more agile than expected, and pilots routinely took advantage if this. Moreover, more equipment was added to F-16s over the years, and the aircraft was even used as a bomber. This resulted in a lot more weight being hung from the aircraft. The end result was fatigue on the aircraft frame and a loss of half its expected flying life. Current estimates are that F-16s will last no more than 4,000 flying hours. Attempts to strengthen F-16s didnt help much, lengthening useful life to 4,500 or 5,000 hours at most. Since the aircraft have to be flown a lot just to keep the pilots in practice, there will be no flyable F-16s in 15 or so years. This can be delayed if the fighter force is reduced. Attempts to repair the damage have failed so far. All of this plays well in the air force, providing another reason to spend more money to build the new F-22 and JSF.