A collapsible crane allowed the submarine to retrieve her floatplanes from the water. Aircraft were launched from a 37-meter (120 ft) catapult on the forward deck forward of the hangar. The conning tower was offset to port to allow the stowage of three Aichi M6A1 Seiran ('Clear Sky Storm') float-equipped torpedo bombers along the centerline.

The cross-section of the pressure hull had a unique figure-of-eight shape which afforded the strength and stability to support the weight of a large, cylindrical, watertight aircraft hangar, 31 meters (102 ft) long and 3.5 meters (11 ft) in diameter, located approximately amidships on the top deck. Until the commissioning of the United States Navy ballistic missile submarine USS Benjamin Franklin (SSBN-640) in 1965, the I-400-class were the largest submarines ever commissioned. Measuring 122 m (400 ft) long overall, they displaced 5,900 t (6,504 short tons), more than double their typical American contemporaries. The I-400-class submarines had four 1,680 kW (2,250 hp) diesel engines and carried enough fuel to circumnavigate the world one-and-a-half times. Until 1965, the Sentaku-type submarines - I-401 and her sister ships I-400 and I-402 - were the largest submarines ever commissioned. Capable of carrying three two-seat Aichi M6A1 'Seiran' (Mountain Haze) float-equipped torpedo bombers, the Sentoku-class submarines were built to launch a surprise air strike against the Panama Canal. I-401 ( 伊号第四百一潜水艦, I-gō-dai yon-hyaku-ichi-sensuikan) was an Imperial Japanese Navy Sentoku-type (or I-400-class) submarine commissioned in 1945 for service in World War II.

1 × 14 cm/40 11th Year Type naval gun.

8 × 533 mm (21 in) forward torpedo tubes.

I-401 world of warships submarines 2018