We cannot say with any degree of certainty how wide-spread boxing exercises were among all the U.S. Army infantry training camps during W.W. II, but the attached photo-essay will cue you in to the fact that it was mighty important at Camp Butner in 1943:
"Every man has fear of the unknown and if he does not know what physical combat is he will fear it. Mass boxing overcomes this natural reluctance... The idea is to develop the fighting heart. The entire boxing program is is directed to this goal."