During World War I, he served on the destroyer Whipple (DD-15) and the cruiser Chattanooga (CL-18) where he saw duty in the Eastern Atlantic and in European Waters.

Promoted to Lieutenant Commander he was assigned as Assistant Naval Attaché in Tokyo, Japan, and upon completion of that duty he returned to sea as Navigator on the carrier Enterprise (CV-6).

[3] Before the United States entered World War II, Ofstie served on staff duty on the carrier Yorktown (CV-5) in 1940.

[3] In August 1944 Ofstie was promoted to rear admiral and was assigned as Commander Task Group 32.7/Carrier Division 26 with his flag in the escort carrier USS Kitkun Bay (CVE-71) for the invasion of Palau in September.

[3] Keeping his flag in Kitkun Bay, Carrier Division 26 moved to the Philippines to support the Battle of Leyte Gulf.

[3] Rear Admiral Ofstie's last sea command in World War II was as COMCARDIV 26 at the Invasion of Lingayen Gulf, Philippines, in January 1945.

[3] In 1946, Ofstie was assigned to the Joint Chiefs of Staff Evaluation Group and served at the nuclear tests at Bikini Atoll.

[3] On 11 October 1949, Rear Admiral Ofstie testified before a committee and stated, "strategic air warfare, as practiced in the past and as proposed for the future, is militarily unsound and of limited effect, is morally wrong, and is decidedly harmful to the stability of a post-war world."