Sentence:  <WSD>Broken</WSD> Arrow refers to the U.S. military's code word used during the Vietnam War. This call was used only in the direst of tactical situations, when a ground unit was overrun by enemy forces. When "<WSD>Broken Arrow</WSD>" was heard on the radio nets, all available aircraft were diverted to provide close air support for the endangered command. 
Meaning of the word marked with <WSD> tags:  a code phrase that a ground unit is facing imminent destruction from enemy attack and all available air forces within range are to provide air support immediately.