What does broken arrow mean in the military?

In the Vietnam era, the code words "broken arrow" was a call for close air support by all available forces for a military unit on the ground in grave danger of being overrun and destroyed by the enemy. In later years it became a code word for any type of accidental event involving nuclear components or weaponry which is not likely to start an immediate nuclear war. In 1996 John Travolta starred in a movie titled "Broken Arrow" in which terrorists steal nuclear warheads from the U.S. military.