The Frankford Arsenal was a US Army ammunition plant in Philadelphia, Pennsylvania, operating from 1816 to 1977. It played a vital role in developing and testing military weapons and ammunition, including early cartridge systems, the Maynard priming system, and the Frankford friction primer. The Arsenal was a self-contained entity, with its own facilities and services, and it was a key contributor to the nation's military preparedness during the Civil War and both World Wars.