Arnold Marcus (26 June 1892 – 27 July 1917) was an officer in the United States Navy during World War I.
Born in Atlantic City, New Jersey, Marcus was appointed a midshipman 22 May 1909. He assumed command of submarine A‑7, 13 March 1917. On 27 July 1917, Lieutenant (jg.) Marcus died from injuries suffered during an explosion on A‑7, while the submarine was on patrol in Manila Bay, Philippine Islands. He was the last man to leave the ship, remaining on board to ensure the safe evacuation of his crew and to attempt the grounding of his ship to prevent sinking.
The destroyer, USS Marcus (DD-321), was named after Marcus.