The Viper was a submachine gun designed by Derek Hutton-Williams.
The Viper first appeared in 1945. It was designed to meet the GS Specifications of the time. Chambered for 9x19mm Parabellum, the Viper utilized MP-40 magazines and had a rate of fire of 692 rounds per minute. The fire selection system was unconventional; instead of a fire selector switch, the Viper had a lever on the left side of the body that could be pushed inwards. If pushed inwards fully, the Viper could fire in fully-automatic mode, and if pushed half-way then it would fire in single shots only. If not pushed at all, the safety would be engaged. The trigger guard was enlarged for arctic usage. Only three Viper submachine guns were made, each with different barrel lengths, but only two of these weapons were actually trialed. It was rejected due to its excessive rate of fire, and also because it was very slightly overweight. No further attempts to improve the design were ever made.