Answer: ackack

AnswerCrossword Clue
ACKACKAntiaircraft fire
ACKACKAntiaircraft fire, informally
ACKACKWWII defense
ACKACKAnti-aircraft fire.
ACKACKSound of gunfire.
ACKACKAir-raid gun
ACKACKAir-defense fire
ACKACKKind of gun
ACKACKGun aimed at a bomber
ACKACKAnti-aircraft gun's onomatopoeic nickname
ACKACKWWII gun