Armament
The ships had torpedo launchers moved to the middle of the hull. This made available the required large space in the bow for the BQQ-2, BQQ-5 in modernized boats, sonar system, a new and powerful detection low-frequency sensor. Initially armed with Mark 37 torpedoes, they later carried the improved Mark 48, the UGM-84 Harpoon (replacing four of the Mk-48s) and the UUM-44 SUBROC (replacing six Mk-48s, four after Harpoon was adopted). The maximum weapons load was 23 torpedoes/missiles or, theoretically 46 Mk-57, 60 or 67 mines. Or a mix of mines, torpedoes and missiles.
Read more about this topic: Thresher/Permit Class Submarine