▁types ▁of ▁son ar ▁g ear ▁were ▁added ▁to ps ide . ▁Thus ▁equ ipped , ▁Gr ou per ▁depart ed ▁Port sm outh ▁on ▁ 2 3 ▁June ▁ 1 9 6 0 ▁to ▁emb ark ▁on ▁the ▁fourth ▁phase ▁of ▁her ▁long ▁career , ▁research ▁vessel ▁for ▁the ▁Naval ▁Research ▁and ▁Under water ▁Sound ▁Labor ator ies . ▁Her ▁duties ▁as ▁a ▁floating ▁labor atory ▁took ▁her ▁frequently ▁to ▁the ▁Car ib bean ▁and ▁B erm uda , ▁although ▁she ▁retained ▁New ▁London ▁as ▁her ▁home ▁port ▁and ▁engaged ▁in ▁operations ▁there ▁and ▁as ▁far ▁north ▁as ▁Nova ▁Scot ia . ▁Her ▁efforts ▁were ▁focused ▁on ▁the ▁study ▁of ▁sound ▁propag ation ▁in ▁water . ▁In ▁December ▁ 1 9 6 2 , ▁Gr ou per ▁entered ▁the ▁Philadelphia ▁Naval ▁Sh ip yard ▁for ▁over ha ul ▁and ▁modification ▁to ▁prepare ▁for ▁further ▁work ▁in ▁this ▁field . ▁Gr ou per ▁left ▁the ▁Philadelphia ▁Naval ▁Sh ip yard ▁in ▁May ▁ 1 9 6 3 ▁to ▁res ume ▁her ▁investigation ▁of ▁water bor ne ▁sound . ▁▁▁ 1 9 6 4 ▁– ▁ 1 9 6 8 ▁ ▁In ▁June ▁ 1 9 6 4 , ▁Gr ou per ▁was ▁awarded ▁the ▁Battle ▁E ffic iency ▁" E ". ▁In ▁November ▁ 1 9 6 5 , ▁the ▁sub marine ▁again ▁entered ▁the ▁Philadelphia ▁Naval ▁Sh ip yard ▁for ▁over ha ul ▁and ▁equipment ▁modifications ▁to ▁increase ▁her ▁useful ness ▁as ▁a ▁floating ▁under water ▁sound ▁labor atory . ▁She ▁depart