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 <WSD>regiment</WSD> had assaulted the beachhead of Leyte during World War 2 , , the 7 th Cavalry was not in the best fighting condition . 
Meaning of the word marked with <WSD> tags:  army unit smaller than a division