Japanese Submarines in World War II: Operations and Impact

The Imperial Japanese Navy entered World War II with one of the world’s most advanced submarine fleets, boasting a variety of designs from midget submarines to massive underwater aircraft carriers. Despite their potential, Japanese submarines, or "I-boats," had a mixed record due to doctrinal focus, operational challenges, and Allied countermeasures. This blog delves into their role in the Pacific Theater, their successes, failures, and the broader implications for the war.

The Japanese Submarine Fleet: A Diverse Arsenal

Japan’s submarine force was highly varied, reflecting their ambition to dominate the Pacific. By 1941, the IJN had around 60 operational submarines, growing to 176 by the war’s end. Key types included:

• I-400 Class: The largest submarines of the war, over 400 feet long, capable of carrying three Aichi M6A Seiran aircraft for long-range strikes. Only three were completed, intended for missions like attacking the Panama Canal.

• Type B1 Submarines: Equipped to carry a reconnaissance seaplane, these subs conducted operations as far as the U.S. West Coast, including the shelling of an oil refinery near Santa Barbara by I-17 in 1942.

• Kaiten Human Torpedoes: Introduced late in the war, these were suicide weapons piloted by a single crewman. They had limited success, sinking the fleet oiler USS Mississinewa in November 1944.

• Midget Submarines: Used in the Pearl Harbor attack, these small subs aimed to penetrate harbors and sink key ships but often failed due to navigational issues and detection.

The IJN’s submarines were technologically advanced, featuring the Type 95 torpedo (a smaller version of the "Long Lance"), which was highly effective with its oxygen-fueled propulsion. However, their strategic deployment often limited their impact.

Key Operations and Achievements

Japanese submarines participated in several notable operations, achieving some successes but often falling short of their potential:

• Pearl Harbor Attack (December 1941): Five midget submarines were deployed to support the air raid. None achieved significant damage, and most were lost or captured, highlighting early operational flaws.

• I-19’s Devastating Salvo (September 1942): The Type B1 submarine I-19 launched a spread of six torpedoes at a U.S. convoy, sinking the aircraft carrier USS Wasp, damaging the battleship USS North Carolina, and sinking the destroyer USS O’Brien in a single attack—one of the most successful torpedo salvos of the war.

• Yanagi Missions (1942–1944): Japan and Nazi Germany conducted submarine trade missions to exchange strategic materials and technology. Submarines like I-29 and I-30 carried gold, blueprints, and even personnel (such as Indian nationalist Subhas Chandra Bose in 1943). Only four missions succeeded due to Allied interception.

• Attacks on the U.S. Mainland: Submarines like I-17 and I-25 conducted small-scale attacks on the U.S. West Coast, shelling coastal targets and launching incendiary bombs via seaplane to ignite forest fires in Oregon. These caused minimal damage but heightened American fears of invasion.

Despite these efforts, Japanese submarines sank about 1 million tons of Allied merchant shipping (184 ships), a fraction compared to the U.S. Navy’s 5.2 million tons or Germany’s 14.3 million tons.

Strategic and Doctrinal Challenges

The IJN’s submarine strategy was heavily influenced by its doctrine of fleet warfare, which prioritized supporting the main battle fleet over independent commerce raiding. This focus led to several issues:

• Focus on Warships Over Merchant Shipping: Unlike U.S. and German submarines, which targeted supply lines, Japanese subs were often tasked with attacking enemy warships to weaken fleets before a decisive battle. This limited their impact on Allied logistics.

• Supply Missions: By 1943, many submarines were diverted to resupply isolated island garrisons, such as at Guadalcanal. These missions were inefficient, with subs ill-equipped for cargo transport, and resulted in heavy losses.

• Lack of Radar and Coordination: The IJN was slow to adopt radar technology, only installing it on submarines late in 1944. This left them vulnerable to Allied detection, especially during nighttime surface operations.

The rivalry between the Japanese Army and Navy further hampered effectiveness, as resources and priorities were misaligned, often at the expense of submarine operations.

Allied Countermeasures and Japanese Losses

The Allies, particularly the U.S. Navy, developed effective anti-submarine warfare (ASW) tactics that decimated the IJN’s submarine force:

• U.S. Submarine Campaign: American submarines crippled Japan’s merchant fleet, sinking over 5 million tons of shipping, which starved Japan’s war economy. Japan’s ASW efforts were inadequate, with poor coordination and late adoption of technologies like airborne radar and large-depth charges.

• Air and Surface Patrols: By 1944, U.S. destroyers and aircraft hunted Japanese submarines relentlessly. For example, the USS Wahoo, commanded by American ace Dudley “Mush” Morton, was sunk by Japanese aircraft in October 1943 after sinking 19 ships.

• Codebreaking and Intelligence: Allied codebreaking efforts, such as the Ultra program, allowed them to track and intercept Japanese submarines, particularly during Yanagi missions.

Of the 176 Japanese submarines operational during the war, around 130 were lost, many to Allied ASW efforts or operational accidents like the sinking of USS Tang by its own torpedo in 1944, which led to the capture of American ace Richard H. O’Kane.

The Role of Weather in Submarine Operations

Weather conditions in the Pacific Theater posed additional challenges for Japanese submarines:

• Monsoons and Typhoons: Operating in the Indian Ocean and near the Japanese home islands, submarines faced heavy storms that disrupted surface operations and made navigation difficult, especially for smaller vessels like midget subs.

• Cold Climates: In northern waters, such as around the Aleutian Islands, harsh winters caused equipment failures and strained crews, who were often inadequately equipped for prolonged exposure.

• Visibility Issues: Fog and rain reduced visibility, complicating reconnaissance missions and seaplane launches, such as those attempted by I-25 off the U.S. coast.

While these conditions affected both sides, the IJN’s reliance on surface operations for battery recharging and aircraft launches made them particularly vulnerable.

Legacy and Post-War Fate

As the war ended, Japanese submarines faced varied fates. Some, like I-36, survived despite poor luck with faulty torpedoes, while others, like I-47, were scuttled by the Allies in 1946 as part of Operation Road’s End. The I-400 class was captured by the U.S. Navy, studied for its advanced design, and later scuttled to prevent Soviet access during the Cold War. The legacy of Japanese submarines influenced modern naval warfare, particularly in the development of submarine-launched aircraft and missile systems.

Conclusion

The Imperial Japanese Navy’s submarines were a technological marvel, from the massive I-400 class to the desperate Kaiten human torpedoes. However, their impact was limited by strategic missteps, doctrinal focus on fleet support, and effective Allied countermeasures. While they achieved notable successes, such as I-19’s devastating attack on USS Wasp, their overall contribution paled in comparison to Allied submarine efforts. The story of Japanese submarines in World War II is one of ambition, innovation, and ultimately, missed opportunities—a fascinating chapter in naval history.