The T-38 radar had a range of about 30 km and could track aircraft traveling at up to 700 mph (1100 km/h).

The United States is eager, however, to use a new command and control center in Saudi Arabia to track aircraft.

They monitor radar screens to track aircraft.

But radar, which tracks aircraft by reflected radio waves, became the biggest threat.

Transponders, which allow air traffic controllers to track aircraft, were switched off in some cases in the Sept. 11 hijackings.

Once airborne, the plane can track friendly and enemy aircraft over a 300-mile radius.

There is a radar station which tracks civil aircraft.

Controllers use this information to track aircraft and keep them a safe distance from each other.

The researchers also hope to use satellites to track civilian aircraft all over the world, replacing radar.

Operators use the displayed information primarily for navigation and to track other vessels and aircraft.