My F-I-L flew 32 mission over Germany and Yugoslavia in 1944. He told of his crew getting tired of all that shooting during training. A plane would pull a target behind attached by a long cable. After landing bullet holes were counted in the pulled target. The gunners would shoot for the cable that attached the pulled target. Though they could not see the cable the knew it was there and with enough 50 caliber bullets in the air one was bound to hit the cable. When this happened training was over for the day and everyone got off early.