Introduced in 1918, the Model 51 was developed from patents and designs from John D. Pederson of Pederson Device and Irwin-Pederson fame as a hesitation-locked blowback semi-automatic pistol with multiple overlapping safety features and good ergonomics. Fixed sights, with the two line address and patent markings (1920-1921 with "OTHERS PENDING") on top of the slide, with the serial number on the left side of the frame, "AS" on the trigger guard, niter blue finished small parts, and checkered and riveted grips with "REMINGTON/UMC/TRADE MARK" in circles at the top. Included with the pistol is a black Remington-UMC box with white, black and red labels (hand-numbered on one end label).