The U.S. Air Force is trying to figure out how to cope with future combat zones where their UAVs will be operating in a more hostile environment. These fears come from two sources. First, there's increased enemy firepower. In the 1990s, the air force encountered this during the air campaign against Serbia. Of the 17 aircraft lost, 15 were UAVs. The Serbs had more anti-aircraft guns and missiles, and were more aggressive in using them against UAVs.
The second problem, which the air force does not want to discuss in detail, is the electronic link between the UAVs and their controllers. The air force uses a satellite link for its larger (Predator and Reaper) UAVs. There have been increasing problems with people jamming, or otherwise messing with signals between satellites and the ground. The air force apparently believes this situation will get worse. They are working on it, but not talking about it. Makes sense.
Today's UAVs are basically the same as those flying in the 1990s. That is, they are slow, unstealthy, propeller driven aircraft. Flying at altitudes between 3,000-6,000 meters (10-20,000 feet), the UAVs can be seen, and are sitting ducks for mobile anti-aircraft systems. Some of these can reach as high as 6,000 meters. Typical of these is the Russian 9M311 (SA-19). These missiles have a ten kilometer range against air targets, and can hit targets at up to 8,300 meters (26,000 feet). The missile weighs 40 kg (88 pounds) and has a 9 kg (20 pound) warhead These missiles are commonly found in a light armored vehicle (Tor M1), that also carries 30mm cannon (that can hit aircraft as high as 3,200 meters) and a radar.
Some air force commanders point out that heavy losses would be suffered in such an environment, even if Hellfire equipped UAVs hunted down and destroyed many of these mobile anti-aircraft systems. The air force is looking into this opportunity as well. No point in waiting for it. Best to have a few surprises ready for any future foe.
Air force commanders are also concerned about the larger number of pilots needed to operate UAVs (each one requires 2-3 operators to keep them up there). The problem is that UAVs stay in the air longer than manned aircraft, and thus need more pilots. Operating a UAV is easier (physically and psychologically) than piloting a manned aircraft. But the big problem in the air force is their insistence on using officers as UAV operators, while the other services will use NCOs. The air force only recently began training non-pilots to operate UAVs. The air force was compelled to go this way because there were simply not enough pilots available for UAV operator duty. The air force is automating more of the "piloting", something that has been going on for manned aircraft as well.