"Sennet" was fitted out by 18 September. She held training exercises and torpedo-tube testing off the coast of Connecticut and Rhode Island until 22 October. The submarine then tested mines and torpedoes for the Mine Warfare Test Station, Solomons Island, Md. On 11 November, "Sennet" proceeded to the operations area off Balboa, C. Z. and conducted further training exercises. The submarine departed Balboa on 29 November for Pearl Harbor and arrived there on 16 December 1944.