Nonetheless, the boat was the fastest submarine in the world underwater when built,[1] beating the previous record set by the similar World War I-era British R-class.

[1] For surface running, the boat was powered by a single 1,200-brake-horsepower (895 kW) diesel engine that drove one propeller shaft.

On the surface, Submarine No.71 had a range of 3,830 nautical miles (7,090 km; 4,410 mi) at 12 knots (22 km/h; 14 mph); submerged, she had a range of 33 nmi (61 km; 38 mi) at 7 knots (13 km/h; 8.1 mph).

[1] 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.