Normally found in equipment boxes along with the Sapper's tools.
In Commandos 2: Men of Courage , the Nazi soldiers dressed in light blue/grey carry the MP40. All combat characters can use it once the soldier is nuetralized. It is the only machine gun in Commandos 2 and 3 and it is ideal for close range combat especially when hiding behind a wall. It can also be fired outside windows although by doing so you are easily detectable.
If the enemy is moving fast the MP40 is generally inaccurate.
Generally it should only be used to kill enemies that are impossible to kill silently.
Interestingly in the Asian and South-Pacific missions in Commandos 2 it can be found randomnly in boxes although this is rare.