Assault Gun is a set of free wargames rules by David Kershaw. David writes:
This rule set is designed to allow players to simulate large actions of the Second World War using miniature models. Each division is represented by less than 10 bases (regiments and battalions), so players can command several divisions each, and play a recognisable action of the Second World War.
The rules originally were available on Yahoo Groups, but with that site shutting down in 2018, I have archived the files here.