antiaircraft fire vs firing

antiaircraft fire and firing both are nouns.

Word	Noun	Adjective	Verb	Adverb
antiaircraft fire	Yes	No	No	No
firing	Yes	No	No	No

As nouns, firing is a hypernym of antiaircraft fire; that is, firing is a word with a broader meaning than antiaircraft fire:

Other hypernyms of antiaircraft fire include fire.

antiaircraft fire (noun)	firing (noun)
firing at enemy aircraft	the act of setting something on fire
	the termination of someone's employment (leaving them free to depart)
	the act of discharging a gun
	the act of firing weapons or artillery at an enemy