The smart bomb has caused another change in how air forces operate. The first big change was to greatly reduce the number of bombers or fighter bombers needed to support the troops. One or two smart bombs can destroy a target, where otherwise, from a few dozen, to over a hundred dumb (unguided) bombs would be required. With smart bombs, fighter bombers don't have to go in low to drop dumb bombs. While at low altitude, fighter bombers are vulnerable to enemy weapons, and at risk of flying into the ground, or the side of a mountain.
With smart bombs, a half dozen fighter bombers and bombers can cover all of Afghanistan. And that's why aerial tankers are now finding it necessary to go to the aircraft that need more fuel, rather than having the fighters come to the tankers. With so few aircraft patrolling the skies, waiting for troops below to request a smart bomb, or a low altitude gun run or "show of force" (a fighter or bomber coming in low and loud over a Taliban position often scares the enemy into fleeing), you can't really afford to pull an aircraft away to go to the tanker. It's easier to have the tanker answer a call for fuel.
For over half a century, the drill was that the tankers would set up a location in the air, where they would fly in circles, and aircraft needing fuel would call ahead, make an appointment, then show up to get their fuel. This approach was used because it kept the tankers safe from enemy attack, and out of heavily trafficked air space. In Afghanistan, there is no danger of enemy attack.
Currently, the U.S. has three squadrons of tankers supporting operations in Afghanistan. Two are based in the Persian Gulf, while the third operates out of Manus, in Kyrgyzstan. On a typical day, the tankers would fly 52 sorties, and refuel 250 aircraft (some more than once) with 1,500 tons of fuel. The U.S. has two types of tanker aircraft. The KC-135 is based on the 1950s Boeing 707 (actually, the other way around), while the KC-10 is based on the 1970s DC-10 wide body airliner. The KC-10s only comprise 12 percent of the U.S. tanker fleet, but they fly 25 percent of the missions over Afghanistan. That's because the KC-10 can carry more fuel and stay in the air eight hours, compared to six for the KC-135.
The tanker refuel a wide variety of aircraft, including electronic warfare aircraft and transports. But most of the customers are fighters (which need a refill every 90 minutes or so) and bombers (which can stay in the air twice as long before needing more fuel). The tanker pilots work so much that many are grounded before the month is up because they can only spend 150 hours a month in the air. Thus many reserve tankers serve over Afghanistan, and the average tour for a tanker crew is about two months. With the new "go to the customer" policy, the tanker crews are working even harder, since flying to each new refueling requires that they make sure they avoid any military aircraft, and commercial flights as well. There is no nationwide ATC (Air Traffic Control) in Afghanistan, although some AWACS aircraft are being sent to set an improvised system up. Apparently there have been some close calls, and these may have involved tankers going from job to job.