Born in Boston, Massachusetts 01 October 1882, Allen Melancthon Sumner, Jr., initially went to Harvard before securing a place in the Naval Academy. On 17 March 1907, Sumner was commissioned a Second Lieutenant in the Marine Corps. Until 1909 he was stationed in turn at the Marine Barracks of the Naval Academy, Annapolis, Maryland, and Norfolk Navy Yard. He was then ordered to Cuba with the 1st Provisional Regiment of Marines in the Army of Cuban Pacification. In December 1909, he served on temporary duty on USS Prairie. He retired on January 1, 1914, after seven years service.

Sumner was recalled as soon as war was declared in April 1917, and began serving on active duty at Marine Barracks, Quantico, on 05 July 1917. When the 1st Machine Gun Battalion (MGB) was formed in August, Sumner was assigned to 81st Company. Sumner's war record is as follows: Sailed from New York on 14 December 1917, on USS DeKalb, arriving in St Nazaire on 31 December. Sumner trained in the Vosges and was in the front lines in March at Mont-sur-la-Cote on the Verdun Front. On 29 April, relieved Major Waller in Command of 81st Company when Major Waller was transferred to the 3rd Division to command the 8th MGB. Participated in the action at Belleau Wood and when Major Cole was wounded on 10 June, and Captain Major became battalion commander in his stead (himself to fall five days later), Sumner took his place in command of the right front.

Captain Sumner's death occurred a month later on 19 July, at Vierzy, near Soissons, where the 6th MGB was to take part in the attack on Tigny. He was hit by a fragment of a High Explosive shell and killed instantly. Later it was debated whether he had instead fallen during an air raid. Captain Sumner received the Croix de Guerre with Gilt Star as well as 3 Silver Star Citations. He is buried in Plot A, Row 13, Grave 25 in the American Cemetery at Belleau.