Artillery comes in 2 forms in Il-2: ground artillery for attacking ground targets, and anti-aircraft guns of all calibers.
Ground Artillery[]
Ground artillery does exactly what you think it does, it targets ground targets. This can cover anything from an infantry mortar to the 105mm howitzer to the titanic 600mm Karl Gerät mortar.
Anti-Aircraft Guns[]
Anti-aircraft target anything that files, although they will target ground targets too. Anti-aircraft guns in Il-2 can be ground mounted, vehicle mounted, or ship mounted. Anti-aircraft guns range from the small single and quad Maxim gun mount to the Wirbelwind quad 20mm, to the Bofors 40mm, to the 5 inch/38, 105mm, and 150mm guns found on ships.
Some of the more common anti-aircraft guns seen in Il-2 are:
Flak 30: Single 20mm
Classification: Light anti-air gun, ground mount
Danger factor: 8
Flak 38: Quad 20mm
Classification: Light anti-aircraft gun, ship mount
Danger factor: 10
Wirbelwind: Quad 20mm
Classification: Light anti-aircraft gun, vehicle mount
Danger factor: 10
Type 96: Single, dual, or triple 25mm
Classification: Light anti-aircraft gun, ground or ship mount
Danger factor: 6
Flak 43: Single or dual 37mm
Classification: Medium anti aircraft gun, ground or vehicle mount
Danger factor: 8
QF 2 pounder (AKA pom-pom gun): Quad or eight mount 40mm
Classification: Medium anti-aircraft gun, ship mount
Danger factor: 7
Bofors L/60: Single, dual, or quad 40mm
Classification: Medium anti-aircraft gun, ground or ship mount
Danger factor: 10
Type 88: Single 75mm
Classification: Heavy anti-aircraft gun, ground mount
Danger factor: 5
"Eighty-Eight": Single 88mm
Classification: Heavy anti-aircraft gun, ship or ground mount
Danger factor: 9