On an early November day in the skies over southern Indiana, Maj. Steve Stilwell of the Missouri Air National Guard's 131st Fighter Wing was honing his air-to-air combat skills. As he threw his F-15 into a turn, he stressed his big Eagle at two to three times the force of gravity, a relatively gentle maneuver in the world of dogfighting. But it proved to be more than the 27-year-old fighter could handle: It began to shake violently, paralyzing Stilwell's left arm, and then the fuselage shattered just behind the cockpit. As the rear bulk of the plane fell away, Stilwell shot forward. "I kept telling myself: I gotta get out, I gotta get out," Stilwell remembered to the St. Louis Post Dispatch. "I found the ejection handle. .  .  . I am a little concerned why a plane would break in half."

Stilwell isn't the only one. Four days later, the Air Force grounded its fleet of F-15Cs--about 450 aircraft--and not for the first time. The grounding remains in effect. The fighters, approaching an average age of 30 years, "have become serious maintenance challenges as they get older, and now I'd suggest that we may be facing a crisis," says Lt. Gen. David Deptula, the former F-15 pilot who is the Air Force's head of intelligence. Deptula also reports that his pilot son is flying the very same F-15 that he flew in the late 1970s.

Stilwell's story tells you a lot about the state of the U.S. military, and especially its equipment. The old gear is wearing out. Like a lot of other major weapons platforms in all four services, the F-15C is a design from the late Cold War that's pulling frontline duty decades beyond what was originally planned. The new gear--in this case, the F-22 Raptor--is being bought in far smaller numbers and years later than intended. And, in an almost impossibly perverse twist, production of the F-22 comes to an end with the 2008 budget, at just 183 planes. The air superiority mission these fighters perform, regarded as an American birthright for generations, is suddenly an open question: After the Stilwell crash, at a time when Russian bombers have resumed Cold War-style patrols, the Canadian Air Force volunteered its F-18s to help police the skies over Alaska. One wonders if the Canadians or other allies would be so helpful over Iran or the Taiwan Strait.

The fact is that, despite committing--correctly, in our view--the United States to an ambitious security strategy, the Bush administration has not done enough to build the force that can carry out that strategy.

How can this be? As we are told over and over again, the United States is now spending in real, inflation-adjusted dollars more money on defense than at any time since the Vietnam war. And isn't the U.S. defense budget larger than those of all the major powers of the world combined? How much is enough?

Well, even the short answer has five parts. First, we now have an all-volunteer force that costs a lot more when it comes to personnel, insurance, housing, and retirement benefits than our previous draft-heavy force. Unless Americans and their representatives in Washington want to return to conscription, which no one except Rep. Charles Rangel seems ready to do, fielding a force is just going to be a lot more costly. Second, the weapons and platforms we buy are fewer in number, and partly as a result we ask them to do more. That in turn drives costs up. Third, one reason we spend more than others is that with the major exception of China virtually everyone else cut spending at the end of the Cold War and has kept cutting. Fourth, unless we want a whole different global security order, the burden of keeping the peace in the world remains largely in America's hands, as manifest in the fact that we have gone to war multiple times since the fall of the Berlin Wall. And, finally, yes, we do spend a lot, but we are also fighting two wars.