The U.S. Air Force has ordered 982 Digital Anti-jam Receiver (DARs, GPS receivers that will work even if they are being jammed) for some of its transport aircraft. The DARs cost $38,000 each. There are several ways you can defeat attempts to jam GPS signals. Some of the methods are well known, others are classified. No one has successfully used GPS jammers in combat yet, but the potential is there. Some of these DARs will equip the air force special operations (commando) aircraft and helicopters.