Type 91 torpedo

Type 91 torpedo
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Name	Type 91 torpedo
Type	Aerial torpedo
Origin	Empire of Japan
Service	1931–1945
Used by	Imperial Japanese Navy Air Service
Wars	Second Sino-Japanese War, Pacific War
Designer	Kure Naval Arsenal
Design date	1928–1931
Production date	1931–1945
Launch platform	Aichi D3A, Nakajima B5N, Mitsubishi G4M

Type 91 torpedo. The Type 91 was a family of aerial torpedos developed and deployed by the Imperial Japanese Navy during the interwar period and World War II. It was the primary aerial torpedo used by the Imperial Japanese Navy Air Service in the early years of the Pacific War, most famously during the attack on Pearl Harbor. Designed to be launched from various carrier-based and land-based aircraft, the weapon evolved through several modifications to improve its performance and reliability in combat.

Development and design

The development of the Type 91 began in the late 1920s at the Kure Naval Arsenal, driven by the Imperial Japanese Navy's evolving doctrine for aircraft carrier warfare. Japanese strategists, influenced by theorists like Isoroku Yamamoto, prioritized the aerial torpedo as a key weapon for sinking capital ships. The design team, led by engineers from the Naval Technical Department, faced significant challenges in creating a torpedo that could be reliably dropped from aircraft at high speed and low altitude without breaking up upon water entry. Key innovations included a wooden stabilizer attachment to control its descent and a mechanism to reduce its initial running depth, preventing it from diving too deep and missing its target. Extensive testing was conducted in the Seto Inland Sea and later in the shallow waters of Kagoshima Bay, which simulated the conditions of Pearl Harbor.

Operational history

The Type 91 torpedo first saw combat use during the Second Sino-Japanese War, deployed by aircraft from the aircraft carrier Kaga against Chinese shipping. Its most historically significant employment occurred on December 7, 1941, during the attack on Pearl Harbor. Torpedo bombers like the Nakajima B5N, launched from carriers including Akagi and Sōryū, used modified Type 91 Model 2 torpedoes fitted with wooden fins to successfully attack the USS Oklahoma and USS West Virginia in the shallow harbor. The weapon was also used with devastating effect in other major naval engagements of the early war, including the Battle of the Java Sea, the Indian Ocean raid, and the Battle of the Coral Sea. Its use declined later in the Pacific War as Allied anti-aircraft warfare and air superiority reduced the effectiveness of torpedo bomber attacks.

Technical specifications

The specifications varied across models, but common features defined the series. The Type 91 typically used a kerosene-fueled wet-heater engine, driving contra-rotating propellers. The warhead contained a high-explosive charge, initially Type 97 explosive and later more powerful formulations. Guidance was provided by a gyroscope and a depth-keeping mechanism. For the critical Pearl Harbor operation, the Model 2 modification was essential; it included large wooden stabilizers to prevent the torpedo from porpoising or diving too deep in the shallow confines of the anchorage. This modification allowed a successful drop from an altitude as low as 20 meters and at aircraft speeds approaching 200 knots, a technical achievement that surprised Allied naval experts.

Variants

The Type 91 was produced in several major variants, each denoting an improvement or adaptation. The initial **Type 91 Model 1** entered service in 1931. The **Type 91 Model 2**, introduced in 1936, featured improvements to the engine and the critical shallow-water attack modifications. The **Type 91 Model 3**, developed later, had a heavier warhead and enhanced speed. The final major production variant was the **Type 91 Model 7**, which incorporated a simpler, more reliable oxygen-enriched air flask system for greater speed and range. There were also sub-variants and field modifications, such as different fin configurations for launches from specific aircraft like the Mitsubishi G4M land-based bomber.

See also

* Type 93 torpedo * Type 95 torpedo * Nakajima B5N * Attack on Pearl Harbor * Battle of Midway

Category:Torpedoes of Japan Category:Aerial torpedoes Category:World War II naval weapons of Japan