The Revolution in Close Air Support- The war in Afghanistan revealed a new, and very useful, way to supply close air support (CAS) for ground troops. CAS had something of a golden age during World War II, when there were plenty of fighter-bombers overhead and they all belonged to the army (the separate air force did not arrive until after World War II). The single engine fighter-bombers were often in radio contact with the ground troops, having been assigned to support a specific unit. The aircraft would provide information about what was up ahead, and the ground troops could call for specific ground targets to be strafed (attacked with the aircraft's machine-guns) or bombed (most fighter-bombers of that era could carry two or four 500 pound bombs.) After World War II, the air force became a separate organization and replaced it's slower prop driven fighters with faster jets. While the jets could carry more bombs, their higher speed made it more difficult to drop the bombs precisely. This was especially true when enemy ground troops were around, often firing at you as your jet fighter-bomber came in at nearly 200 meters a second, trying to fly the plane, find the target and avoid ground fire all at once. The air force began to move away from providing this kind of support. The army was buying more helicopters and jet fighter-bombers became more expensive and fewer. By the end of the 20th century, the U.S. air force rarely delivered World War II style CAS, and usually only with their shrinking number of A-10 aircraft. 

All this changed during the 2001 Afghanistan war. 

U.S. special forces troops with the anti-Taliban forces were in constant communication with aircraft overhead, ready to bring down bombs when Taliban resistance was encountered. The 2,000 pound bombs were favored, as past experience (going back to World War II) showed that only very thick cement fortifications could withstand such a weapon. The Taliban had neither the resources nor the time to build such fortifications, so they were systematically blown out of their earthen bunkers and trenches. Unlike World War II, where 2,000 pound bombs dropped by heavy bombers landed hundreds of meters from their intended target, smart bombs hit within 30 meters of their targets over 95 percent of the time (and not much farther than 30 meters when they "miss.") Thus during World War II, it took several dozen 2,000 pound bombs to do what one can do now, because so many of them would miss the target. Moreover, back then, you had to keep friendly troops farther away to avoid getting hit by the wayward bombs. During World War II, low flying fighter-bombers like the P-47 could drop 500 pound and 1,000 pound bombs with more accuracy, but those smaller bombs were less likely to take out enemy fortifications and the aircraft were more likely to be damaged or shot down by ground fire. Smart bombs using GPS, or guided by laser designators on the ground, are a lot more accurate than even the low flying P-47s (which were in turn more accurate than the low flying jet fighter bombers that had to move at a higher speed during their bomb runs.)

This new technique was enormously effective. Because the friendly troops could be as close as half a kilometer from the enemy target, they could quickly move in and take the enemy position before the foe could rush in reinforcements. But it got better. The bombs could be dropped by heavy bombers far overhead, out of range of enemy guns or portable missiles. A B-52 or B-1 can carry two dozen 2,000 pound GPS guided bombs. The guys on the ground can move up to an enemy position, call in a few bombs to blow away the entrenched enemy and then go in and finish off the dazed survivors. No more problems with overworked pilots coming in fast, trying to figure out who is where and getting shot at in the process. Moreover, a 2,000 pound bomb will also disable (if not outright destroy) tanks and other armored vehicles. 

All this makes life a lot more difficult for enemy ground forces who dont have any air force or long range surface to air missiles in working condition. The U.S. air force still has to begin any war by going after these targets, Once they are gone, the guys on the ground can pound the enemy with the one ton bombs. This approach cracked ground defenses time after time in Afghanistan and there's no countermeasure for the technique on the horizon.