A product of the 1960s, the Model 137 Gyrojet uses a miniature solid fuel rocket in place of a standard cartridge. As the rocket does not need a solid chamber or extractor equipment, the entire pistol can be greatly simplified and made from lightweight materials. The Model 137 was the earliest of the Gyro Jet models, and was manufactured in far fewer numbers than the later Mk I and Mk II. The Model 137 was also the model that was submitted for U.S. military trials for the Vietnam War. This example has standard markings and features and no visible serial number, meaning it may be a pre-production example.