She returned to Hawaii in June 1965 and remained in the vicinity until February 1966, which earned the ship a Navy Unit Commendation. During her 1966 western Pacific cruise, which began on 17 February and ended on 29 August, she returned to the combat zone off Vietnam as well as fulfilling a schedule of Seventh Fleet exercises and port visits. Upon her arrival back to Oahu, the submarine began an extended period of operations in the islands, broken by a major overhaul of 17 months' duration. That overhaul included radical modifications to her hull structure during which she was lengthened by to receive the PUFFS passive sonar installation.