During the Spanish–American War, he served in Admiral Dewey's Squadron at the Battle of Manila Bay.

He commanded both the battleship North Dakota (BB-29) and the armored cruiser South Dakota (ACR-9), and served as Director of Target Practice and Engineering Competitions for the Navy Department before the United States entered World War I.

[1] In July 1918, he designed and oversaw the building and was in command of the five Naval Railway Batteries in France.

Plus the French legion of honor He later commanded Destroyers, U.S. Atlantic Fleet, and served as Chief of Staff at the Naval War College; as President of the Board of Inspection and Survey; and as Commandant of the New York Navy Yard and the 3rd Naval District.

[1] Retiring in 1928, Rear Admiral Plunkett died in Washington, D.C., on 24 March 1931.