broken arrow

Short definition from Wiktionary

Noun

1. 1
   A callout marker that consists of a dashed line with an arrowhead.
2. 2
   Used other than figuratively or idiomatically: see broken, arrow.
3. 3
   An accidental event that involves nuclear weapons or nuclear components but does not create the risk of nuclear war.

Phrase

1. 1
   A code phrase indicating that a ground unit is facing imminent destruction from enemy attack and all available air forces within range are to provide air support immediately.