On 10 September 1957, "Marsh" entered the San Francisco Naval Shipyard for overhaul, then went in reserve. Before decommissioning, she conducted two cruises, one to Mexico and one to Hawaii. On 16 August 1958, she decommissioned at San Diego, but remained in service as an anti-submarine training ship of the Selected Reserve Forces. Based at Long Beach, California, she conducted training cruises for selected reserve crews and when they were not embarked served as a training ship for other Naval Reserve units in the Long Beach-Los Angeles area.