After shakedown training out of Port Royal, Great Sound, Bermuda, Osterhaus departed New York on 21 August 1943 for Espiritu Santo, New Hebrides Islands.

For the next two days the two destroyer escorts sent fire and rescue parties on board the merchant ship, finally succeeding in quelling the flames and salvaging ammunition, ordnance equipment and engineering tools.

The following day the transports entered Agat Bay where Osterhaus witnessed concentrated dive and level bombing by American aircraft on Orote Peninsula and the effective heavy shelling by U. S. warships.

The duty of protecting logistic ships operating from Seeadler Harbor in support of the Philippine Campaign continued until 20 November when Osterhaus left that port astern for the Hawaiian Islands and the west coast of the United States.

She departed Kwajalein Lagoon on 16 September bound with Escort Division Eleven for Pearl Harbor, San Diego, the Panama Canal, and New York City where she received Navy Day visitors on 27 October.