Assault is a class in Day of Defeat: Source.
The Assault class is excellent for close quarter combat environment. Crouch down to increase the SMG's accuracy in long range. Don't understimate the accuracy of the SMG you are using while crouching.
The Assault class is best used for clearing buildings, is vulnerable to Machine Gun nests and snipers. The smoke grenade is a good way to get across a street or into a building being watched by an MG or sniper.
While holding the Thompson or MP40, your secondary button (M2) is a punch. Punching isn't quite as effective as a knife or shovel, but can be very useful in desperate close quarters combat.