(Scanned from Polmar and Carpenter's "Submarines of The Imperial Japanese Navy")

This was the most numerous class of Japanese submarines.  These boats were fast, long-ranged, and carried a seaplane, which could be launched on a forward catapult.  However, I-17 carried the catapult aft, and her hangar opened aft as well.  During the war, the aircraft facilities were removed from some boats in order to mount a second 14cm gun.  In 1944, I-36 and I-37 were modified to carry four Kaiten, and I-36 was later modified again to carry six Kaiten.

They were used extensively and had their share of successes.  On 31 August 1942, I-26 damaged aircraft carrier USS Saratoga with one torpedo hit (out of six launched), removing her from the Guadalcanal campaign at a critical time.  Two weeks later, on 15 September, I-19 achieved an incredible success when she fired six torpedoes at aircraft carrier USS Wasp.  Two of these hit the carrier forward and ignited gasoline storage, dooming the ship.  The remaining four torpedoes of this salvo went several thousand yards further and encountered a second American carrier task force, damaging battleship USS North Carolina enough to require two months to repair, and sinking destroyer USS O'Brien.  This was among the most damaging torpedo salvoes in history.  On 13 October, it was again the turn of I-26 as she finished off USS Juneau, one of several damaged and unescorted American cruisers which survived the First Naval Battle of Guadalcanal the evening before.  The loss of life on USS Juneau was extreme, including the five Sullivan brothers.  Bagnasco credits all of the Type B boats (B1, B2, and B3 combined) with sinking 56 merchant ships of 372,730 GRT.

Of these 20 boats, 95% were lost during the war, and only I-36 survived.  I-15 was lost off San Cristobol on 2 November 1942 to destroyer USS McCalla.  I-17 was sunk by New Zealand trawler Tui and 2 US Navy aircraft off Noumea on 19 August 1943.  I-19 was probably lost to attack by US Navy aircraft on 18 October 1943.  I-21 was lost to aircraft from escort carrier USS Chenango on 29 November 1943.  I-23 was an operational loss in February of 1942.  Destroyer USS Patterson sank I-25 off the New Hebrides on 3 September 1943.  I-26 survived until October 1944, when she became an operational loss off Leyte.  I-27 was sunk by HMS Paladin and HMS Petard off Addu Atoll on 12 February 1944.  I-28 was torpedoed by submarine USS Tautog south of Truk on 17 May 1944, and I-29 received similar treatment from USS Sawfish in Balintang Channel on 26 July, 1944.  A mine claimed I-30 off Singapore on 13 October 1942.  I-31 was lost to destroyers USS Edwards and USS Farragut off Kiska 12 May 1943.  I-32 was sunk by destroyer escort USS Manlove and PC 1135 south of Wotje 24 March 1944.  I-33 was an operational loss during sea trials in the Inland Sea 13 June 1944.  I-34 was sunk by submarine HMS Taurus off Penang 13 November 1943.  Destroyers USS Meade and USS Frazier sank I-35 off Tarawa 23 November 1943.  I-36 was the sole survivor among this class, and was scuttled off Goto Island 1 April 1946.  Destroyer escorts USS Conklin and USS McCoy Reynolds sank I-37 off Leyte 19 November 1944.  I-38 was lost to destroyer USS Nicholas south of Yap 12 November 1944, while destroyer USS Boyd eliminated I-39 in the Gilberts 26 November 1943.