The Spitfire is a firearm with an interesting importance in legal history. Originally designed and marketed as an open-bolt semiautomatic-only carbine, it was determined to be a machine gun under the law in 1968, and all examples were required to be registered or destroyed. The reason was not its open bolt design, but rather because the safety lever could be used to hold the sear down and allow fully automatic fire without any alteration to the gun. This example was duly registered, and it now a transferrable machine gun.

Aside from this brouhaha, the Spitfire was simple a very poor man's Thompson lookalike - although functionally it is much more like the M3 Grease Gun than the Thompson. It uses M3 magazines, and is cocked by simply pulling the bolt back with a finger, like the M3A1. The construction is extremely crude. Following its machine gun ruling, a series of very similar guns were produced by the same designer which used a closed bolt operating system to avoid the legal issues - the Volunteer carbine in particular.