[1] During World War II, Greenslade stirred up controversy, during his service at Mare Island Naval Shipyard, when urged that American-born and alien Japanese be excluded from areas of strategic importance.

[3] Among his classmates were future admirals such as Claude C. Bloch, Harry L. Brinser, Cyrus W. Cole, Charles E. Courtney, Frederick J. Horne, Alfred Wilkinson Johnson, Edward C. Kalbfus, Henry E. Lackey, Edgar B. Larimer, Joseph K. Taussig, Adolphus E. Watson and Clark H.

He graduated as Passed Midshipman in August 1898 with Bachelor of Science degree and was attached to the gunboat USS Concord, operating along the coast of Bataan, Philippines during the Philippine–American War.

Greenslade participated in the patrols in North Atlantic until July 1904. when he was transferred back to the United States Naval Academy for duty as an instructor in the Department of Physics and Chemistry.

[4][1] He was subsequently attached to the battleship USS Maine and served as senior Watch officer under Captain William B. Caperton until August 1909, when he was ordered back to the United States Naval Academy for his second tour as an instructor in the Department of Physics and Chemistry.

[2][1] He served in this capacity until the end of January 1918, when he assumed command of newly commissioned minelayer USS Housatonic at Bethlehem Shipbuilding Corporation in Hoboken, New Jersey.

[5][6][1] Greenslade was appointed commanding officer of protected cruiser USS Galveston in March 1919 and participated in the transports of British-American troops from Harwich to Murmansk, USSR as part of Allied intervention in the Russian Civil War there.

Greenslade stirred up controversy, during his service at Mare Island Naval Shipyard, when urged that American-born and alien Japanese be excluded from areas of strategic importance.

[12][1] Following the United States entry into World War II, Greenslade assumed additional duty as commander, Western Sea Frontier and was promoted again to the temporary rank of vice admiral on May 1, 1942.

His new duty consisted of the sea defense of the Pacific coast of the United States and Mexico and the Eleventh, Twelfth, and Thirteenth Naval Districts were subordinated to his command.

[1] Vice admiral John W. Greenslade died on January 6, 1950, in his hometown, aged 69 and was buried with full military honors at United States Naval Academy Cemetery.

[18] Greenslade was married three times: his first wife Marie Melanie died in 1936 and he had two sons from their marriage, John Francis (who also served in the Navy and retired as rear admiral) and Robert Wills.