On 16 April 1965 Mispillion was placed in commission in reserve as she prepared for a prolonged "jumboization" conversion and overhaul, begun at Toledo, Ohio, in April 1965, and completed at Boston, Massachusetts, in August 1966. With an increased capacity of over , an added length of almost 100 feet (30 m), and over 50 additional crew members, in addition to modern equipment, Mispillion departed Boston on 6 September 1966 to return to her home port at Long Beach, California.
