Here's something to contribute to the list of submachineguns:
Reising M55 SMG
Something I consider to be a very cute and neat looking gun with an unfounded bad reputation. The Reising is often derided as an unreliable, finicky gun that was a consistently poor performer, and a large part of this reputation is taken out of context for what the Reising was. When it was first manufactured the Reising was intended mainly for police and civilian guards, giving something that was both more potent than a pistol while still very light and easy to have on your person. It was accurate, light, reasonably ergonomic, and quite easy to shoot. In many respects it was superior to the M1 Thompson.
However, it was never intended to fill a military role, and when placed into one out of desperation more than anything, it came up short. But again, it was a civilian gun, designed to be pleasant to shoot rather than to endure the harshness of the battlefield. There is nobody really at fault for the Reising's poor performance in combat, as the USMC was desperate for short range firepower suited to the jungles of the Pacific, and a faulty submachinegun was better than no submachinegun at all. And it is not as if Eugene Reising should be chastised for designing a civilian gun to meet civilian requirements either!
Probably one of my favorite lesser known weapons of WW2, for both it's unique looks and unique story.
EDIT: Accidentally mis-scaled the drawing and had to redo it, based on pictures of the weapon side-by-side with the Thompson my original was about 30% too large.