In General Orders No. 13, 23 November 1887, by authority of the Secretary of War, officers of the Corps of Engineers were authorized to carry on boats belonging to the engineer works under their charge, a square scarlet flag, with a white castle in the center. These flags corresponded to those of the battalions of the engineers.
The original flags authorized for general officers were boat flags, scarlet in color. They were first authorized in War Department General Orders No. 4 dated 22 August 1903, for use of officers of the Army when making official visits to Navy vessels. The same provisions for boat flags were promulgated in Article XXVIII, paragraph 232 of Regulations for the Army of the United States, 1904, with amendment dated 31 December 1905. These same provisions were listed in Article XXVIII, paragraph 236 of Regulations for the Army of the United States dated 1908 as amended by War Department General Order 128 dated 12 August 1908, and the same provisions in paragraph 240 of the 1910 regulation for the Army of the United States.
The authorization of flags was further expanded to include automobile flags and field/office flags in 1923. Line officers had scarlet flags, staff officers normally had branch colors and branch insignia. Army Medical Corps General Officer flags were maroon with white stars and when the Chief of Chaplain position was established as a General Officer in 1941, a dark blue flag with white stars was authorized. In 1947, the Deputy Chief of Staff for Personnel authorized all General Officer flags except Medical Corps and Chaplain flags to be scarlet with white stars and gold fringe. Medical General Officers kept the maroon with white stars and the Chaplain flag was changed from dark blue to the ecclesiastical purple color with white stars in 1952.