Penetrating into the Bonin Islands–East China Sea area, Haddock attacked a freighter on the surface on 22 August, sinking troop transport Tatsuho Maru (6334 tons).

Tatsuho Maru had suffered engine trouble and had fallen back; being left behind by her convoy making her easy prey for the new boat and crew.

In the Formosa Straits on 26 August Haddock fired four stern shots at Teishun Maru (formally Vichy French Tai Seun Hong) but missed; the submarine swung around to bring her bow tubes to bear and sent the 2251 ton cargo ship to the bottom.

She was attacked by two destroyers raining depth charges, and when she finally surfaced to clear the area, Haddock found herself surrounded by Japanese patrol craft.

Aerial attack and depth charges kept her from bagging the other members of the convoy and bad weather forced Haddock to return to Midway on 17 February.

Following the torpedo tracks, the corvette dropped 24 depth charges, many directly over Haddock, causing her to lose buoyancy and she descended to 415 ft.

Under the USN's relentless attack, spearheaded by the submarines, Japan's sea lifelines had shrunk to a trickle and targets were scarce, but Haddock succeeded in sinking auxiliary minesweeper Noshiro Maru No.2 (126 tons) on 17 April, before returning to Pearl Harbor on 10 May 1944.

Fitted out with extra deck guns for her eleventh war patrol, Haddock sailed in company with submarines Sennet and Lagarto for the seas east of Japan.

The boats made a diversionary sweep designed to pull early warning craft away from the intended track of a carrier group en route for air strikes against Tokyo.

Gaining their objective with complete success, the submarines attacked the picket boats with gunfire, allowed them to send contact reports, and then sank several, diverting Japanese efforts away from the undetected carrier group.

Haddock spent her twelfth and thirteenth war patrols on lifeguard station near Tokyo, standing by to rescue downed airmen after raids on Japanese cities.

In August 1948 Haddock was assigned duty as a reserve training ship for 6th Naval District, and served in that capacity until being again placed out of service at New London in May 1952.

She was again assigned to reserve training, this time at Portsmouth, N.H., June 1956, and finally was struck from the Naval Vessel Register and sold for scrap to Jacob Checkoway on 23 August 1960.