Transiting the Panama Canal on 17–18 March, she reported for duty with the Pacific Fleet on the latter date, and pushed on for Pearl Harbor, arriving there on 1 April.

Ottawa proceeded alone from Pearl to Eniwetok, Marshalls, and Ulithi, Carolines, then departed the latter in convoy on 27 June 1945 bound for Okinawa.

Following a ten-day buoy availability to clean her boilers, Ottawa embarked elements of the 2nd Marines and their equipment and departed Saipan on 18 September 1945 for Nagasaki and the occupation of Japan.

After disembarking the Marines and their gear at Nagasaki, she sailed for the Philippines in convoy on 26 September, reaching Subic Bay on 4 October.

After discharging occupation troops and gear, Ottawa embarked Army and Navy passengers for transportation back to the U.S., departing Nagoya on 11 November 1945.

She performed routine duties in the lagoon at Bikini until the afternoon of 24 July, when she again departed to observe the shallow underwater detonation (Test Baker) from a vantage point 25 miles to the east.

Proceeding via Jacksonville, Florida, and Bayonne, New Jersey, the ship ultimately reported to Commander, 5th Naval District, for final disposition, reaching Norfolk on 19 December.