Yeah, I heard it as land-based artillery as well. The device was described as a simple metal ring (Monkey Ring) that encircled the pile and stopped the lowest level of balls from moving sideways. BTW, on ships, and possibly in coastal batteries as well, boys and young men were given the job of carting ammunition to the guns, and were called Powder Monkeys, so there is a connection between artillery ammunition and monkeys.

The occasional Folk 'Superband' Brass Monkey described themselves during one of their inactive periods as Cryogenitally Frozen. Ouch!!