The real question is why they're being produced at all. The DDG-51 was originally designed to provide air defense for aircraft carrier battle groups during the Cold War, when there was a severe threat from Soviet planes. The V-22 is an expensive aircraft that is designed to deliver Marines from their ships to shore during an amphibious assault. Its mission could be performed by a helicopter that is half as expensive. The Bush administration attempted to cancel the plane, but the Clinton administration and Congress have embraced it.
Some weapons still being developed are equally unnecessary.
Despite the lessened tensions in the post-Cold War world, the armed services are planning three new tactical aircraft programs, two of which are in development. In a post-Cold War world, the Navy can provide air support to Marine Corps ground forces, eliminating the need for Marines to buy a new aircraft. Defense hawks complain that defense spending has fallen to a little more than 3 percent of the U.S. gross domestic product. But that figure represents only how much of the economy's productive capacity is used up by defense spending. The magnitude of defense spending is better measured by comparing the absolute level of the defense budget with the threat the U.S. faces.