The 6mm Lee Navy is a rifle cartridge developed in the early 20th century for the United States Navy. It was designed by James Paris Lee and was intended for use in the Lee Navy rifle, which was a bolt-action firearm. The cartridge features a bullet diameter of 6mm and was notable for its accuracy and flat trajectory, making it suitable for naval engagements. Although the 6mm Lee Navy was innovative, it saw limited adoption and was eventually replaced by more powerful cartridges. Its design influenced later developments in small arms ammunition, but the rifle and cartridge combination did not achieve widespread military use.