Serving on Mexican Border during the Pancho Villa Expedition, Silverthorn subsequently enlisted in the Marine Corps as a private on 27 April 1917.

During the combats near the village of St. Etienne on 4 October 1918, he carried an important message, at a critical time, to his battalion commander under heavy machine-gun and shell fire, exhibiting extraordinary heroism and disregard for his personal safety.

After the war, Silverthorn remained in the Europe and participated in the Allied occupation of the Rhineland and 'Pershing's Own' E Company, 3rd Army Composite Regiment until September 1919.

At the beginning of May 1923, Silverthorn was assigned to the 1st Brigade of Marines and sent to Haiti in March 1924, where he served as district commander within Gendarmerie d'Haïti at Aux Cayes and later as chief of police at Port-au-Prince.

Silverthorn remained in this capacity until June 1943, when he was assigned to the Army Navy Staff College as Chief of the Amphibious Warfare Section.

Silverthorn was then finally transferred to the Pacific theater and appointed chief of staff of I Marine Amphibious Corps under Lieutenant General Roy Geiger.

At the end of July 1944, Silverthorn participated in the Recapture of Guam and made several trips to the front line positions to secure necessary information and to give assistance and advice to organization commanders.

Silverthorn remained on active service after the war and was appointed to the capacity of chief of staff, Fleet Marine Force, Pacific.

[2] A great honor and also responsibility came in July 1950, when Silverthorn was appointed Assistant Commandant of the Marine Corps, succeeding Major General Oliver P. Smith in this capacity.

Final duties came in February 1952, when he was appointed commanding general of the Marine Corps Recruit Depot Parris Island, South Carolina.

Lieutenant General Merwin Hancock Silverthorn died of cancer on 14 August 1985, in Bethesda Naval Hospital, Maryland and is buried in Arlington National Cemetery.