GR translation: staggering on/chug

[Mike Jing]

V96.31-36, P98.25-30   Spitfires come roaring in low over the dark sea at
suppertime, the searchlights in the city staggering on, the after-hum of
sirens hangs in the sky high above the wet iron seats in the parks, the AA
guns chug, searching, and the bombs fall in woodland, in polder, among
flats thought to be billeting rocket troops.

Here "staggering on" means "turning on in a staggered manner", is that
correct? The published translation interprets "staggering" as "wavering",
which seems wrong to me.

And "chug" means the AA guns are firing, right? I understand as a noun it
means the sound it makes while firing. The published translation interprets
it as the sound the AA guns make by just turning, which I think is
incorrect.