in the Caribbean followed for Grouper. During this period, she chalked up two "firsts": in 1946 she became the first submarine to have a Combat Information Center installed, and the following year she effected the first discharge and recovery of men from a submerged and underway submarine. 1950 – 1957 These operations ended 5 March 1950 as Grouper entered the Mare Island Naval Shipyard for conversion under project SCB 58 to the Navy's first "hunter-killer submarine". Her classification was changed to SSK-214 on 2 January 1951. With the addition of a snorkel and extensive sonar and radar facilities, Grouper emerged from the yard on 27 June 1951 to pioneer in research on the deadly submarine-versus-submarine warfare. For the next eight years, as a unit of Submarine Development Group 2, Grouper worked to develop and test concepts of hunter-killer antisubmarine warfare. In this duty, she ranged along the East Coast from Nova Scotia to Florida, as well as participating in Caribbean exercises. In 1953 and 1955, exercises took Grouper across the Atlantic to Rothesay, via Iceland. In the fall of 1957, she then participated in NATO maneuvers. 1958 – 1962 Grouper was reclassified AGSS-214''', 17 May 1958, and on 28 November 1959 she entered the Portsmouth Navy Yard for extensive modification. Her forward torpedo room was converted into a floating laboratory; work benches and additional berths for scientists were installed, and various types of sonar gear were added topside. Thus equipped, Grouper departed Portsmouth on 23 June 1960 to embark on the fourth phase of her long career, research vessel for the Naval Research and Underwater Sound Laboratories. Her duties as a floating laboratory took her frequently to the Caribbean and Bermuda, although she retained New London as her home port and engaged in operations there and as far north as Nova Scotia. Her efforts were focused on the study of sound propagation in water. In December 1962, Grouper entered the Philadelphia Naval Shipyard for overhaul and modification to prepare for further work in this field. Grouper left the Philadelphia Naval Shipyard in May 1963 to resume her investigation of waterborne sound. 1964 – 1968 In June 1964, Grouper was awarded the Battle Efficiency "E". In November 1965, the submarine again entered the Philadelphia Naval Shipyard for overhaul and equipment modifications to increase her usefulness as a floating underwater sound laboratory. She departed Philadelphia on 1 May 1966, reached New London