One of the clearest "lessons learned" from Operation Iraqi Freedom is that traditional assumptions about the proper "tooth-to-tail" ratio--that is, the proportion of forces that do the actual fighting to those that support combat operations--need to be rethought. It is likewise clear that this will require changes in the way the Defense Department procures its weaponry.

Operation Iraqi Freedom scored a very large military victory with a very small fighting force, on a vast battlefield measuring tens of thousands of square miles. By any standard, we suffered very few losses and very little attrition along the way, arriving in Baghdad on Day 21 as ready to fight as on D-Day.

Thus, in Iraq, the limits on American military power were defined less by the tooth than by the tail. Consider the air campaign: On an average day, about 1,500 sorties were flown, of which only half were actual strike sorties. More than one-quarter were refueling missions--over 9,000 tanker sorties in total.

Without these tanker aircraft, projecting and sustaining air power would not be possible. While longer-range bombers and cruise missiles hit some Iraqi targets, the overwhelming majority of the strike sorties were flown by the shorter-range, tactical aircraft that depend on midair refueling. These swarms of fighter-bombers, along with close air support aircraft, were the key to the flexible, air-ground coordination at the heart of the new American way of war.

Refueling tankers likewise kept open the northern front in Iraq. After Turkey refused to open its borders to a coalition ground force, U.S. commanders had to rely upon a mix of air power and a small number of Special Forces to turn the tide in the north. Aircraft from the Mediterranean were able to reach into Iraq only because of tankers based in Romania and Bulgaria.

In Afghanistan, too, where the Pentagon relied even more heavily on air power, our ability to extend operational range with airborne refueling made all the difference. A mission of B-52s flown out of Guam, for instance, required 48 support tankers. Any future operations in northeast Asia--over the Korean Peninsula or the Taiwan Strait--would not be possible without extensive refueling support. In short, U.S. airpower would not be a global force but for the ability to conduct aerial refueling.

Unfortunately, the defense drawdown of the 1990s did real damage to less-glamorous support forces like aerial refueling. The average age of KC-135 tanker aircraft is more than 40 years old--or more than 10 years older than the rest of the Air Force fleet. At any given time, about one-third of the KC-135 fleet is out of service for repairs, and the "E" model spends an average of 400 days in costly depot-level maintenance.

Indeed, tankers risk being the Achilles' heel of American airpower. Just as the requirements for long-range power projection are increasing, the resources to enable them are increasingly insufficient. As outgoing Air Force Secretary James Roche put it: "My fear is that our tanker fleet could be the [lost] horseshoe nail that could cause the horse to tumble, the king to fall, and the kingdom to come apart."

Although the Air Force has devised an innovative proposal to assure an adequate tanker fleet, it has become bogged down in bureaucracy. If ever there were an argument that traditional business practices are ill-suited for defense "transformation," the saga of the tanker-leasing proposal would count as People's Exhibit A.

The problem is this: The Air Force's approved, pre-9/11 procurement program contained no real money to replace aging tankers or--better still--expand the fleet to meet growing requirements. Mr. Roche's clever solution, familiar to every American who has leased his or her automobile rather than purchasing it outright, was to lease 767 tankers as efficient "gas stations in the sky." Even better, the Air Force could acquire the new tankers outright when the term of the lease is complete, or anytime in between.

Perhaps inevitably, this new approach to procurement riled the bureaucracy, with the General Accounting Office--charged to take the narrowest possible analysis--concluding that "the urgency of [tanker] replacement is unclear." After all, until Sept. 11, the Air Force never mentioned the need for tankers in its annual "unfunded requirements" list.

It takes a special government green-eyeshade mentality to miss the urgency of the tanker requirement. Government calculations almost always are based on straight-line projections that the future will be just like the past; but big events like the war on terrorism simply cannot be quantified in this way. And if Sept. 11 does not reasonably generate new "requirements," nothing does.

Some in Congress have also grumbled about the tanker-lease innovation. Even some lawmakers who have strongly supported rebuilding America's defenses take a narrow and disparaging view of the Air Force's proposal. Maybe they have--but have not yet revealed--a better way to meet the urgent need for extending the effective range of the Air Force that protects us.

We would be wise to invest more in long-range bombers--more B-2s, for example--since the ability to operate globally on short notice will be vital to winning the war on terror. In the meantime, however, let's make the most of the fleet we have by supporting it properly.

Thomas Donnelly and Richard Perle are resident fellows at the American Enterprise Institute.