Loose File it may be, but Ack Ack was what I was taught on Group I in 1964. Usually used for walking up roads during a move, WWII style. Ack Ack Platoon, leapfrogged the sections forward.
We still had a lot of WWII Vets in, who absolutely insisted to get off the objective as soon as it was cleared. They were fanatical about it from the bitter experience of being stonked by the Germans.