Finnish Boats

Yes, Finland did have a submarine or two in World War II.

27 October 1942 the Finland sub. IKU-TURSO under command of Kapitanleutnant Pakkala attacked an unknown Soviet submarine which actually was attacked the evening of 26 October. The Soviet submarine dived when IKU-TURSO opened fire on her with the deck gun but shortly after midnight on 27 October, the Soviet submarine surfaced and was immediately sunk by one torpedo and combined fire from the deck gun of IKU-TURSO. This was probably the Soviet submarine SC-306 but could also have been SC- 320 or SC-304. This was the only action by IKU-TURSO in World War II.

I.J.N. Submarines

24 October 1944 the I.J.N. submarine I-56 under command of KK M. Morinaga claimed a sunken American transport but the American LST 695 was only damaged by this attack.

25 October 1944 I-56 fired five torpedoes at an American carrier & a destroyer. The 12,000 ton carrier USS SANTEE was damaged, but no indication of any hits on any other ships.

27 October 1944 I-56 reported sinking three American transports in a convoy, but no confirmation.

April 1945, I-56, now under KK Masada, was ready to launch her KAITENs against American ships at Okinawa but was sunk before she could do so. The Japanese Staff assumed there were successes, but no confirmations.