Slitherine

Artillery units were incorporated in corps sized units. The exeption was USSR who had formations with concentrated artillery. We have therefore added shock armies to the USSR which are regular corps units, but with stronger shock attack (artillery) and ground attack (tank units added to formation). The number of shock armies possible for USSR is set in general.txt and is currently at 5. 4 shock armies arrive in November 1941 for free for USSR.

Shock armies have a separate image, corps units with the Katyusha rockets in the background. NATO image is the corps unit with a big dot in the center.

For the other countries you will see that artillery is a separate tech increasing the shock attack of ground units.

What is the difference between hills and forested hills?

The only difference is that air units have lesser ground and shock attack values. So defenders in forested hexes take less losses from air attacks. No difference regarding ground attacks.