"Tambor" sailed from Fremantle on 18 February 1943 to carry out a special mission in the Philippine Islands, in support of "MacArthur's Guerrillas". On 5 March, she landed a small party headed by Lt.Cdr. Charles Parsons with 50,000 rounds of .30 (7.62 mm) ammunition, 20,000 rounds of .45 ACP (11.4 mm) ammunition, and $10,000 in currency on southern Mindanao. On 22 March, she fired three torpedoes at a tanker southwest of Apo Island. {This was the "Bugen Maru", which was damaged} Seven days later, she scored one hit on a freighter out of three torpedoes fired and believed it sank; it was not confirmed. The submarine returned to Fremantle on 14 April for refit in which a 20-millimeter gun was installed forward of the bridge.