I-400 class SubmarineNovember 6, 2018
Research That Puts You on the Edge of Your SeatMay 10, 2019
As Commander Iura walked around the I-405 and first gazed upon the submarine, his first thoughts were: She’s a monster. As large as a small cruiser. With his erect, five-foot athletic frame, a stoic face displaying a prominent nose, gibbous black eyes, and a thin, clipped mustache, he marched around the boat like a Bantam rooster lording over its yard of hens. He was in love with the black leviathan.
As Iura continued his walk, he observed the sub’s sail was at least three stories tall. Her overall length was 400 feet, with a 23-foot beam, and she displaced 6,560 tons submerged. I-405 had a maximum surface speed of 18-knots and could travel 37,500 nautical miles without refueling. She could carry 1,750-tons of diesel, more than enough fuel to reach the United States moving east across the Pacific or west through the Indian Ocean into Atlantic, and return home. And she carried enough provisions for 120-days at sea for her complement of 156 sailors, aviators, and aircraft maintenance crews. No American submarine was comparable, he thought.
Her armament was just as impressive. She had eight forward torpedo tubes and carried twenty Type 95 torpedoes; each with a 1,210-pound warhead that could travel 13,000 yards, which was three times the range of the American Mark 14 torpedo. The most unusual aspect of the I-405, however, were the three Aichi M6A1, Seiran, special-attack planes, secured in a watertight hanger. Each Seiran could carry a 1,760-pound bomb; the largest aerial bomb in the Japanese arsenal.
Iura thought, I-405 could do very little damage to a large US city, but it could easily take out the Golden Gate Bridge in San Francisco.
The most out-of-place looking part of the I-400 class submarine was the round, 102-foot long aircraft hangar that extended over the deck of the boat. At twelve feet in diameter, the hanger was capped with a cone-shaped outer door secured by a two-inch rubber gasket to make the seal watertight. The attack aircraft moved from the interior of the hanger on catapult rails that ran the length of the hanger. After the Seiran bomber rolled out of the hanger, its wings rotated ninety degrees hydraulically and locked into flight position. Crews could then attach the two pontoons and have the aircraft readied for takeoff in under fifteen minutes.
Extending forward from the hangar was an eighty-five-foot long pneumatic catapult. The compressed air catapult could launch the four-ton, two-seat, low-winged monoplane, powered by a 1,410-horsepower Daimler-Benz DB 601 liquid-cooled V12 engine, down the length of its foredeck. As the catapult approached the bow, it rose on a five-degree incline to give the aircraft additional lift. Each Seiran carried a crew of two: a pilot that acted as the bombardier, and a navigator that served as the radio operator and gunner.
On top of the aircraft hangar was three Type 96 triple-mount 25-millimeter (mm) or one-inch anti-aircraft cannons, two positioned aft and one forward of the conning tower, and a single 25-mm anti-aircraft cannon positioned aft of the bridge. The cannons could fire 220 rounds per minute; each shell weighed over five pounds. A single Type 11, 140-mm or five-inch deck gun was located aft of the hangar. The gun’s 84-pound projectile could reach a target over nine miles away.
At the top of the sail lay the bridge or a small open platform, used for observation during surface operations. Towering behind the bridge where the submarine’s radio antennas, two periscopes, and two radar antennas. One of the radar antennas was the Mark 3 air search radar, capable of detecting aircraft out to a range of forty-three miles, the second, held two horn-shaped antennas for the Mark 2 search radar, used to locate surface ships. It included a non-directional antenna for passive radar detection and an omnidirectional antenna which served as a direction finder for target-detection. The two 40-foot periscopes where of German origin; one was for daytime use and the other for nighttime observation.
To counter the drawback of being the largest submarine every built and having a considerable radar signature, the sub had two anechoic coating on its hull. The layer above the waterline absorbed radar waves, and the layer below the waterline was for protection from eco ranging sonar. The anechoic coating also helped to dampen and reduce any sounds emanating from inside the submarine while submerged. The subs four diesel engines were rated at 2,250 horse-power and drove two propellers to a top speed of 18-knots on the surface, and up to seven-knots submerged.
It didn’t take Commander Iura long to conclude that the I-405 would be challenging to maneuver, just due to her size. Another problem he noticed was the submarines sail, the tower-like structure that housed the bridge. The sail was offset to port by seven feet to make room for the hanger. He knew that this would cause the submarine to be permanently out of balance, and the helmsman would have to steer up to seven-degrees to starboard to navigate a straight course which was equivalent to flying an aircraft in a cross-wind. The offset sail also meant that the submarine would require a larger turning radius when turning to starboard.
In the end, Commander Iura concluded that despite the submarine looking like an awkward, lumbering giant, she was, in fact, a fast, well-armed, and best of all a quiet warship. He also concluded that his secret mission in the I-405 was to be one-way; he knew that Captain Furutani and the Japanese intelligence czar, General Tsukuda, expected him to be a Kamikaze or Divine Wind, and sacrifice his boat and crew after the mission. Even if the submarine did make it through the American network of naval defenses and complete its purpose, it was not supposed to make it back to Japan. It would be as if the I-405 and its submariners never existed.