open fire

open fire (third-person singular simple present opens fire, present participle opening fire, simple past and past participle opened fire)

(idiomatic) To begin firing (weapons) at something or someone.
In warfare, whoever opens fire first has a greater chance of victory.
- 2011, James D. Hornfischer, “28: Into the Light”, in Neptune's Inferno: The U.S. Navy at Guadalcanal‎, New York: Bantam Books, →ISBN, retrieved 21 November 2022, pages 273–274:
  The Atlanta was swinging through her own turn to avoid a collision with the van when the searchlight, probably from the destroyer Akatsuki, lit upon her from abaft the port beam. Captain Jenkins reacted as commanders had been trained in peacetime: "Counter-illuminate!" he shouted. His gunnery officer, Lieutenant Commander William R. D. Nickelson, Jr., preferred to respond with other hardware. At once he shouted into his headset mike: "Fuck that! Open fire!" His assistant, Lloyd Mustin, was recording accurate ranges from the narrowcasting fire-control radar and didn't need help from other wavelengths. "Action port. Illuminating ship is target," he instructed his gun captains. Mustin, controlling the after trio of five-inch mounts, and Nickelson slewed their directors onto the lights and opened fire immediately.

to begin firing at something or someone

open fire (plural open fires)

uncovered fire

English