Ack-ack

The army fired upon us with ack-ack.

Ack-acks were set up in the square.

He had thought how down there on the ground, on enemy soil, there were probably hundreds of Ivys, nice Fräuleins with buck teeth and fiancés on U-boats, manning the German ack-ack, all united in an effort to kill him.

The bomber flew through heavy ack-ack.