The U.S. Air Force is under increasing pressure to cut purchases of new warplanes and spend more on air transports and tankers. The air force deployed nearly a thousand transport and tanker aircraft to support the fighting in Afghanistan. These aircraft flew over 27,000 air refueling and transport missions in the first year of Afghanistan operations. The ability to fly troops and material into Afghanistan, and adjacent areas, limited American military operations. This was probably a good thing, as many generals and politicians back in the United States wanted to send in more ground troops early on. But there simply wasn't enough air transport to get them, and their supplies and support troops, there. The air force also learned that, despite the long range of it's most modern warplanes, there were human limits that had to be considered. While B-2 bombers flew missions that took forty hours or more, this proved to be more than the two man crew could safely handle on a regular basis. Same with the two seater F-15s, that flew missions of up to 15.5 hours from bases in the Persian Gulf. Caught between the proven need for more air transport, and the shortcomings of the expensive, new warplane designs, it's still more likely that air force procurement money will go to warplanes, not transports.