Midshipman Giffen graduated with the Academy's class of 1907 and was assigned to the battleship USS Virginia, in which he voyaged around the world with the "Great White Fleet" between late 1907 and early 1909.

Once war formally began for the United States in December, he commanded surface forces that escorted convoys and, at times, operated with the British Home Fleet.

In November 1942, he participated in the North Africa invasion, during which his task force actively engaged French warships and aircraft off Casablanca, Morocco.

During 1943 and into 1944, Rear Admiral Giffen commanded battleship and cruiser task forces in the Pacific, participating in the latter stages of the fight for Guadalcanal (and was the losing commander in the Battle of Rennell Island), the Aleutians campaign, the invasions of the Gilbert and Marshall Islands, and raids against Japanese bases in the central Pacific.

Vice Admiral Giffen was Commander Service Force, U.S. Atlantic Fleet, from August 1945, and retired from active duty at the beginning of September 1946.