IJN I-15 History

The most numerous of all the World War II Imperial Japanese Navy (IJN) submarine classes was the B1-Type, nicknamed the "I-15" class after the first boat launched. Twenty were produced and the I-15 was commissioned on September 30, 1940 at the Kure Navy Yard, Japan. Commander Nobuo Ishikawa was assigned as her commanding officer and remained so throughout her short war time career.

The B1 was 356.5 ft (108.7m) long, her beam was 30ft 5 in (9.3m) wide and the boat's draft was 16 ft 8 in (5.1m). In comparison to the 1940-era Gato American submarine class, the B1 was 45ft longer and had a 3,000 nm greater range as well as faster cruising speeds. Because of the vastness of the Pacific, Japan built boats for extreme range and size, many of which were capable of cruises lasting more than 100 days. In comparison, the Gato class had a maximum of a 75-day patrol.

The B1 (or I-15) had two diesel engines producing 12,400 horsepower (9,200kw) for running on the surface and to charge her batteries for submerged running there was an electric motor producing 2,000 horsepower (1,500kw). This power allowed the boat to operate at roughly 23.5 knots (44km/h) along the surface and 8 knots (15km/h) when submerged. At 16 knots (30km/h) she could cruise 14,000 nm (26,000 km). She required 94 officers and enlisted men and had an additional crew of two pilots that were needed to operate her onboard Yokosuka E14Y "Glen" seaplane used in reconnaissance duties. Some of the class carried this single seaplane, located in a hangar just in front of the conning tower, and was launched by a catapult. One Hundred Twenty-Six of the IJN Type 0 Small Reconnaissance Seaplane (Japanese designation of the aircraft) were built. The E14Y holds the distinction of being the only Japanese aircraft to drop bombs on the United States mainland in all of World War II, this occurring on September 9th, 1942 off the coast of Oregon. Besides a forest fire from the dropped incendiary bombs, no one was hurt and no property was damaged.

The I-15 is assigned to the Fleet (Submarines) under Rear Admiral Sato Tsutomu's command with Vice Admiral Shimizu Mitsumi's Sixth Fleet's Advance Expeditionary Fleet. Under "Operation Z" the I-15 was sent on her first war patrol off the north coast of Oahu on December 7,1941. She received the code signal "Climb Mt. Niitaka", a code indicating war would begin on 12/8/1941 Japan time. Her mission was to sink any warships that came into her patrol area from Pearl Harbor after the initial attack had begun. No ships appeared in her vicinity and I-15 was ordered to return to Japan. On 12/10 she received a signal that an American fleet was sighted nearby, this fleet including the USS Lexington and her escort. Admiral Shimizu ordered six boats to sink the carrier including the I-15. The American fleet was not sighted and she was ordered to proceed to the west coast to attack American ships.

The I-15 was recharging her batteries on the surface when Lieutenant Commander John Tennent's USS Southard (DMS-10), a fast minesweeper, made contact and opened fire with her 4.5-inch main gun. The I-15 submerged and moved in to attack. Ishikawa fired two torpedoes at the minesweeper which both missed their target. DMS-10 acquired the I-15 on sonar and dropped six depth charges in patterns over the next few hours. Now damaged and low on air, the I-15 needed to surface regardless of the situation topside. The USS Southard opened fire from about a mile away with a salvo hitting the I-15's conning tower. The direct hit forced the I-15 to sinks by the bow with all hands on board. She was presumed lost in the Guadalcanal area by the INJ and on December 24th, 1942, her name was officially struck from the naval list. Commander Ishikawa was promoted Captain posthumously in a short career with no recorded enemy ships sunk.

Japan had the most diverse submarine fleet in World War II which is not a surprise considering her island nation status. She built the largest submarines of the day with some over 5,000 tons and over 400 feet in length. She produced midget subs and manned torpedoes as well. Many of the boats could carry aircraft and some even could field multiple bombers. The torpedoes carried on most were the Type 95 series that used kerosene instead of the alcohol used in Allied torpedoes. The IJN fuel mix gave the Type 95 three times the range of their Allied counterparts.

The IJN war plan for boats was to concentrate on warships and not so much merchant vessels as the Americans targeted. So instead of attacking slow unarmed merchant ships Japanese captains attempted to cross swords with well-armed fast surface warships. In comparison, Japan sunk 184 merchant ships during the war while Germany sank 2,840 cargo ships. The US accounted for 1,079 merchant vessels. One would have concluded the IJN should have deployed her submarine fleet off the West Coast of the United States, the Panama Canal and or near Hawaii and India for maximum effect. Instead her boats lurked waiting for the major battleship or aircraft carrier to cross into her patrol zone.

To add insult to injury to the strategy, many boats were also used by the Imperial Japanese Army to resupply island garrisons instead of being used for attack missions. Large submarines were easy to see and were slow to submerge, providing prime targets for enemy warships and dive bombers alike. As a result, many of these Japanese vessels were sunk in these inglorious roles. As the war progressed, losses mounted due to the improved anti-submarine warfare tactics and strategies developed by the Allies. Radar and underwater sonobuoys were consistently dropped by Allied aircraft resulting in the sinking of IJN boats with newly developed acoustic homing torpedoes. The IJN did not develop counter measures or new technological advances in an effort to help protect its submarine force. With mounting losses, moral inevitably declined in the IJN submarine service. It became apparent that boats on 40-day patrols reporting seeing no enemy ships was not due to the lack of allied targets, but the knowledge attacking them was sheer suicide at this point. The IJN submarine service was not prepared, however, to go the way of their Kamikaze brethren in the skies.

IJN I-15 Specification




- Blue Water Operations

- Fleet Support

- Hunter

- Direct-Attack



356.5 ft (108.66 m)

Width / Beam:

30.5 ft (9.30 m)

Height / Draught:

16.1 ft (4.91 m)


Displacement (Surface):

3,655 tons


2 x shafts powered by electric motors generating 2,000 horsepower along with surface diesels generating 12,400bhp.


Speed (Surface):

8 kts (9 mph)

Speed (Submerged):

23 kts (26.47 miles)


13,999 nm (16,110 miles; 25,927 km)


1 x 140mm cannon

6 x 533mm torpedo tubes (all in bow) with 17 x torpedoes.


1 x Yokosuka E14Y1 aircraft

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