The U.S. Navy began operation of a fast-submarine test bed (a boat without combat capability but easily reconfigured to try out various control schemes): the 203-foot USS Albacore, AGSS-569.
USS Cavalla and USS Albacore were both Gato-class submarines ... first as a hunter-killer submarine (SSK-244) and lastly as an "auxiliary submarine" (AGSS-244) before being decommissioned ...