JSTARS, a four engine radar aircraft that can track moving vehicles over as much as 30,000 square kilometers at once, proved very useful during the 1991 Gulf War. But in the Balkans in the late 1990s, and during tests by U.S. army troops assigned to deceive JSTARS, it was discovered that JSTARS could be fooled. In the Balkans, and Afghanistan, the enemy found that they could take advantage of hills, mountains and gullies to hide from JSTARS. Other tricks were discovered as well. A truck dragging 7-10 meters of concertina (rolls of barbed wire) would look like several armored vehicles to JSTARS. Half a dozen trucks could be made to look like a tank battalion. The trucks can then stop, pull the concertina into the truck beds, and take off at a faster speed, and look like a few trucks to the JSTARS. Meanwhile, JSTARS marks the spot where the trucks stopped as a place where tanks are sitting, just waiting for American warplanes to come along and waste their bombs. The trucks can then go pull their scam again and again, limited only by their own imagination. In 1999, the Serbs learned that when there were JSTARS about, they could still move their armored vehicles, or trucks, around in groups of 2-3 vehicles. JSTARS would not always pick up such small groups, and the Serbs could concentrate these small groups of vehicles for an operation without any interference from above. Because of these limitations, the Air Force is eager to have UAVs, equipped with a video camera, to work with JSTARS.