On 9 July 1918, Congress established the rank and grade of warrant officer concurrent with establishing the Army Mine Planter Service (AMPS) within the Coast Artillery Corps. Creation of the Mine Planter Service replaced an informal service crewed by civilians, replacing them with military personnel, of whom the vessel's master, mates, chief engineer, and assistant engineers were Army warrant officers. Warrant officer rank was indicated by rings of brown cord worn on the lower sleeve of the uniform jacket: two for 2nd Mate and 2nd Assistant Engineer, three for 1st Mate and Assistant Engineer, and four for Ship's Master and Chief Engineer.