The Eagle, Globe, and Anchor is the official emblem of the United States Marine Corps. However, its roots can be traced all the way back to as far as 1804, with uniforms of Marines being adorned with brass eagles on square plates. During the War of 1812, this early emblem morphed into an octagonal brass plate embossed with an eagle, an anchor, drums, and flags. As the decades would progress, symbols on the emblem would be replaced with letters. Starting in 1840, Marine uniforms would see the metal letters “U.S.M.” During the subsequent years, more changes, modifications, and additions ensued until in 1868, when Marine leaders believed their insignia too closely resembled that of the U.S. Army infantry, and began to take steps to make a distinctive device. Commandant Brig. Gen. Jacob Zeilin appointed a special board to create a device for the Corps.




Source: Globe trotters and anchor droppers - The History of the Eagle, Globe, and Anchor