Following a Bermuda shakedown, Otter joined the Atlantic Fleet and escorted two carriers to Casablanca, then, for the remainder of the year, she helped protect convoys shuttling from the United States to various Mediterranean ports.

In December 1944, Otter and three of her sister ships formed a task group to hunt and destroy German U-boats in the middle and north Atlantic.

Otter, after playing a crucial role in the depth charge attack, proudly displayed a submarine silhouette on her bridge.

During these operations, destroyer escort Frederick C. Davis (DE-136) was torpedoed and sunk, and while other ships of the group engaged and sank U-546, Otter assisted in the rescue of survivors.

Upon the end of the war in Europe, Otter was one of the ships assigned to accept the surrender of German submarines.