- Antiaircraft artillery.
- The army fired upon us with ack-ack.
- Ack-acks were set up in the square.
2015, Kate Atkinson, A God in Ruins, ISBN 9780385618717, page 140:
- 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.
- (uncountable) Antiaircraft fire
- The bomber flew through heavy ack-ack.
ack-ack (not comparable)
- Of or relating to antiaircraft warfare.