When you know the Brits finally made a good enough gun after two world wars and an interwar period. The Sterling Mk IV features the best of submachine gun designs after the 2nd World War, with its supposedly comfortable stock to cheekweld, better magazine design with its roller follower and controllable (though faster than what the army wanted) rate of fire, the submachine gun was used in many, many conflicts that had any involvement with the commonwealth.
This also comes with suppressed version with its integral suppressor, though lacking the chunky wooden block sadly, but still features a decent firepower for all wet works.
Both submachine guns come with picatinny rails all around the fore with one on the front of the rear sight. Be careful though, it can heat up!
Also comes with 34 round magazine and according to BotR, it can take.... Sten mags!?
Model from Insurgency Sandstorm, thanks WickedBadger!