To the layman, the recently announced Boeing contract to build aerial refueling tankers for the Air Force may sound exorbitant. At $35 billion, it ranks among the largest contracts in Pentagon history, and it comes at a time of steep deficits and government cutbacks.

Commentator Robert Scheer called it “perverse.” In the Truthdig web magazine, Scheer also said, “Defense of the nation, of course, had nothing to do with it, since the end of the Cold War also ended the need for midair refueling of the nuclear-armed bombers intended to retaliate after a Soviet first strike.”

Well, it’s true that the contract has little to do with the Soviet threat. But new aerial tankers have everything to do with the critical function of air mobility. And from the perspective of a user at the pointy end of the spear, I can attest that new tankers are no extravagance.

Just a few days ago I flew an Air National Guard training mission. My crew’s C-5 Galaxy took fuel from a KC-135 Stratotanker, which the new Boeings will replace. For routine paperwork, I wrote down the tanker’s tail number. It started with 57. That’s the year it was built.

Every day (and often in the middle of the night) aircrews depend on these Eisenhower-era tankers. Aviators on their way to Iraq or Afghanistan maneuver their C-17s or C-5s in a precise sky ballet to rendezvous with Stratotankers. This feat of flying skill enables them to take on the gas they need to deliver ammunition, food, medical supplies, and anything else required by American forces.

Why don’t they just put on enough fuel before they take off? Sometimes it’s simply a matter of fuel tank capacity. Sometimes it’s physics: with full fuel and cargo, a plane might be too heavy to take off in the available runway distance. So they put on less fuel, make it off the runway safely, and go meet the tanker.

Since the terrorist attacks of 9/11, we have flown our planes hard. About every ninety seconds, an Air Mobility Command aircraft takes to the skies. To keep our troops supplied, scores of aircraft are aloft at any given moment in what fliers call the “aluminum overcast.” Strategists call it the air bridge. And a critical part of that air bridge has grown far too old.

Air Force mechanics do a marvelous job of maintaining Stratotankers their grandfathers could have serviced. But the hard work and ingenuity of the wrench-turners can go only so far. As any of them will tell you, there are two kinds of machines: those that have broken and those that are going to. The older the aircraft, the more likely the failure.

According to Air Force magazine, the journal of the Air Force Association, a military study has concluded that the U.S. needs 567 aerial tankers to meet current demands. It has only 474, most from the 1950s and early 1960s.

Ultimately, maintaining our air bridge and airlift capability comes down to what happens when nineteen-year-olds get into firefights. Will they have the things they need when they need them?

Apart from airlift, tankers also support other kinds of flight operations: fighters go fast, but they can’t go far without refueling. When those nineteen-year-olds need bigger firepower from above, it comes from fighters, bombers, or attack jets that have remained aloft and at the ready because they’ve refueled in the air.

Additionally, in both wartime and peacetime, transport aircraft refueled by tankers help resupply embassies, respond to natural disasters–and prepare for the next war. No other nation can match our ability to fly troops and supplies in large numbers to any place we need them. This capability doesn’t get a lot of glory, but it gets plenty of respect from potential enemies.

While you read this, a flight crew is somewhere above you, perhaps depending on refueling from an aircraft older than anyone on board. In Baghdad or Kandahar, a logistics officer awaits their cargo, maybe something badly needed by soldiers in the field. The fliers are monitoring their instruments, watching their fuel consumption, and running their rendezvous checklist. From time to time, they’re glancing through the windscreen and looking for that speck in the distance that will enlarge into a flying gas station. And they’re hoping nothing goes wrong.