However, this current itself twists around and around as it flows through the magnetic field, the way a torrent of water twists up a fire-fighter's hosepipe.
The Blue Force Tracker uses satellite signals from friendly forces in the field to map their positions -- reducing the risk of so-called "friendly fire" incidents.
The FBI also has come under fire for not passing along information gathered from field agents in Phoenix and Minneapolis that men of Middle Eastern descent were training in U.S. flight schools.