Her frogmen reconnoitered beaches and reported on suitability of landing Army occupation forces at Shiogama Wan and Ominato Ko, Honshū, Japan.

From 30 September to 7 October 1945, her swimmers made surveys for the Port Director, Otaru, Hokkaidō with the help of United States Army advance parties ashore.

Gantner departed Tokyo Bay on 12 October 1945 to embark a returning Marine contingent at Apra Harbor, Guam, and sailed thence via the Marshalls and Hawaii to San Diego where she disembarked military passengers on 1 November 1945.

From 26 January to 6 March 1946 she made a cruise from San Diego with the 1st Marine Division Reconnaissance Detachment for cold weather maneuvers that took her to Kodiak, Juneau, Tolstoi Bay and Clarence Strait, Alaska.

Departing the last named port on 7 April, she accompanied the escort carrier Rendova (CVE-114) to Yokosuka, Japan, then sailed via Guam and Pearl Harbor for the west coast, arriving at San Diego on 4 May 1949.