Mid-air explosions (or the remaining smoke clouds of those explosions) from ammunition fired by anti-aircraft guns.
![Wikipedia: Mitsubishi_G4M1_bombers_fly_low_through_anti-aircraft_fire[…].jpg](https://commons.wikimedia.org/wiki/File:Mitsubishi_G4M1_bombers_fly_low_through_anti-aircraft_fire_between_Guadalcanal_and_Tulagi_on_8_August_1942_(NH_97766).jpg){kind=link}
![Wikipedia: Mitsubishi_G4M1_bombers_fly_low_through_anti-aircraft_fire_near_a_destroyer[…].jpg](https://commons.wikimedia.org/wiki/File:Mitsubishi_G4M1_bombers_fly_low_through_anti-aircraft_fire_near_a_destroyer_between_Guadalcanal_and_Tulagi_on_8_August_1942_(NH_69117).jpg){kind=link}