Despite the Department of Defense cutback in procurement during the 1990s, major weapons have not, on average, gotten a lot older. The main reason is that about a third of the equipment was retired in the 1990s as the U.S. military shrank after the end of the Cold War. The stuff discarded tended to be the oldest (one exception being the 50 year old B-52). For example, between 1990 and 2000, the average age of air force fighters went from 11 years to 13. Navy warplanes went from 10 to 12 years old. Heavy bombers went from 21 to 23 years. SSNs (attack subs) went from 14 to 13, surface warships went from 16 to 13 and amphibious ships went from 19 to 20 years. The navy and the air force have had to struggle to make a case for new generations of warplanes and ships, mainly because the U.S. Navy is the mightiest on the planet (and in history) and the U.S. Air Force is nearly as dominating in the air.