[6] After conducting shakedown off New England, Haddo departed New London 9 April 1943 to patrol the shipping lanes to Rosneath, Scotland.

When it became clear after three patrols that targets were scarce in this region, Haddo and her sister submarines were sent back to the United States.

Assigned to the Pacific Fleet, she reached Pearl Harbor 25 November and put to sea 14 December on her fourth war patrol, in Philippine waters.

Sailing from Fremantle 29 February, Haddo embarked on her fifth war patrol in waters off Borneo, Java, and Indochina.

For her seventh war patrol Haddo joined a coordinated attack group with five other submarines to cruise Philippine waters.

Japanese convoys ventured into the Palawan area with strong air cover during the day, but usually anchored with escort protection for the night.

As the convoy headed out to sea before daylight 21 August, Ray sank one transport while the escort vessels pursued Harder.

Cruising off Cape Bolinao 23 August, the submarine was about to torpedo a tanker close to shore when she detected a pursuing destroyer.

While turning to avoid a destroyer, Haddo lost depth control, and was not able to regain it in time to effectively attack the cargo ships.

On 22 September, while serving on lifeguard station in Subic Bay,"Haddo" rescued Hollis Hills, a US Navy pilot shot down by antiaircraft fire.

Haddo's skipper decided not to dive and instead turned on a parallel but opposite course, and the frigate shot by with her guns blazing.

In addition to the Navy Unit Commendation, Haddo received six battle stars for her World War II service.