This Colt Service Model Ace was shipped to the King Gun Sight Company of San Francisco, California on October 7th, 1938 in a 2 gun shipment. The letter states the pistol was manufactured 3 days prior on October 4th, 1938.
The D.W. King Gun Sight Company started in the fall of 1928. They were based out of San Francisco, California. They would initially start by making aftermarket sights for Winchester and Smith & Wesson. It would be years later that they would start making sights for Colt. In 1945 D.W. King passed and his widow hired a new manager who alienated a number of key employees. Some left to go on and start the Micro Sight Co. which would eventually end up with a patent infringement lawsuit.
During the King Gun Sight Company's was in business, the company made a variety of aftermarket upgrades nearly all of Colt's Pistol's and Revolvers at the time. This included fixed and adjustable sights, balancing weights, hammers and grips. They also offered a wide variety of gunsmith services alongside the parts. Due to the complex and precise nature of the majority of these parts, King needed to be the company installing these parts directly.