Submarine No.71

Submarine No.71 was an experimental high-speed submarine built for the Imperial Japanese Navy during the 1930s.

Design and description

Submarine No.71 was designed to test high-speed performance underwater. Intended to reach underwater and on the surface, she proved to be too underpowered to reach those goals. Nonetheless, the boat was the fastest submarine in the world underwater when built, beating the previous record set by the similar World War I-era British R-class. She displaced surfaced and submerged. Submarine No.71 was long, had a beam of and a draft of.
For surface running, the boat was powered by a single diesel engine that drove one propeller shaft. When submerged the propeller was driven by a electric motor. She could reach on the surface and underwater. On the surface, Submarine No.71 had a range of at ; submerged, she had a range of at. The boat was armed with three internal bow torpedo tubes; each was provided with one torpedo.

Construction and career

Submarine No.71 was laid down by the Kure Naval Arsenal in December 1937 and was launched that same month by being lowered into the water by a crane. She was completed in August 1938; trials showed that her small size and low-powered diesel made her hard to handle on the surface. While incapable of her intended speeds, she exceeded a submerged speed of 21 knots, almost five years before the famous German German [Type XXI submarine|type XXI] U-boats achieved speeds of around. After extensive evaluations the boat was scrapped in 1940, and the lessons learned contributed to the development of the I-201 [class submarine|Sen Taka]-class, and the Sen Taka Sho-class.