Sentence:  When the Korean war began , on June 25 , 1950 , the anniversary of the day Custer had gone down fighting at the Little Big Horn and the day the regiment had assaulted the beachhead of Leyte during World War 2 , , the <WSD>7</WSD> th Cavalry was not in the best fighting condition . 
Meaning of the word marked with <WSD> tags:  any number of entities (members) considered as a unit