CA-131 was assigned to Joint Task Force 1 operating during "Operation Crossroads". The force was assigned to fleet duty to oversee atomic weapons testing in the Marshall Islands. Fall River sailed to San Pedro, California to receive alterations as needed in order to become the flagship for the upcoming operation. The refit was completed on March 6, 1946 to which then she sailed for Pearl Harbor to accept additional crew including Rear Admiral F. G. Fahrion - commander of the target vessel group for the upcoming tests. Pearl Harbor had long served as a gateway to the Western Pacific and proved extremely vital to Pacific operations of the United States Navy during all of World War 2. Fall River sailed from Pearl and later arrived in the Marshalls by June 14th. During a three week period, a support fleet of 150-plus ships arrived and would provide quarters, nuclear work stations and workshops needed for the 37,000 Navy personnel and 5,000 observers and scientists involved in the atomic program.
Operation Crossroads was to be conducted at the Bikini Atoll in 1946 with the assigned staff on the Fall River, and the supporting USN vessels, investigating the effects of nuclear weapons on naval ships. The series consisted of two detonations each with a yield of 23 kilotons. "Able" was detonated on July 1st, 1946 while "Baker" was detonated underwater on July 25th, 1946. Because of the radioactive contamination delivered by these tests, Bikini Atoll remains uninhabitable to this date though she is regularly visited by sport divers. Participants on Fall River and her task force were thought to be well protected against radiation sickness though testing in the later years revealed crew life expectancy to be reduced by an average of three months.
Fall River returned to Camden, New Jersey in late 1946 for a refit and then, from January 1947 to June 1947, she served a tour of duty in the Far East as flagship of Cruiser Division 1. She received decommissioning orders on October 31st, 1947 and returned to Puget Sound Navy Yard where she was placed in reserve. She was struck from the Naval Register on February 19th, 1971 and sold for scrap on August 28th, 1972. However, some two hundred tons of armor plate from the USS Fall River was removed for use at the Fermi National Accelerator Libratory.
Today, her symbolic remaining bow graces the entrance to "Battleship Cove" in Fall River, Massachusetts.