Japanese submarine aircraft carriers

[Kato]

The Sen Toku I-400-class (伊四〇〇型潜水艦) submarines of the Imperial Japanese Navy were the largest submarines of World War II, and the largest ever built prior to the development of nuclear ballistic missile submarines in the 1960s. These were submarine aircraft carriers and each of them was able to carry 3 Aichi M6A Seiran aircraft underwater to their destinations. They also carried torpedoes for close range combat and were designed to surface, launch the planes then dive again quickly before they were discovered.

I-400, with its long plane hangar and forward catapult

Displacement: 5,223 tons
6,560 tons
Length: 122 m (400 ft)
Beam: 12.0 m (39 ft)
Draft: 7.0 m (23 ft)
Propulsion: 4 diesels: 7,700 hp (5.7 MW), surface
Electric motors: 2,400 hp (1.8 MW), submerged
Speed: 18.75 knots (35 km/h), surfaced
6.5 knots (12 km/h)
Range: 37,500 nmi. at 14 knots
(69,500 km at 26 km/h)
Test depth: 100 m (330 ft)
Complement: 144
Armament: • 3 Aichi M6A1 Seiran sea-planes
• 8 × 533 mm forward torpedo tubes
• 1 × 140 mm (5.51 in) 40 caliber gun
• 3 × 25 mm 3-barrel machine gun
• 1 × 25 mm machine gun

Aichi M6A Seiran.

Members of the US Navy inspecting the plane hangar of I 400

[windrider]

Quite a machine in deed…

In many ways H.I.J.M.S. I-400 was decades ahead of her time. She was the world’s largest submarine, with a length of 120 m, and a surfaced displacement of 3,530 tons. Above her main deck rose a 115 foot long, 12 foot diameter, hangar housing three torpedo-bombers. These floatplanes were rolled out through a massive hydraulic door onto an 85 foot pneumatic catapult, where they were rigged for flight, fueled, armed, launched, and, after landing alongside, lifted back aboard with a powerful hydraulic crane. The I-400 was equipped with a snorkel, radar, radar detectors, and capacious fuel tanks that gave her a range of 37,500 miles: one and a half times around the world. She was armed with eight torpedo tubes, a 5.5 inch 50 caliber deck gun, a bridge 25mm antiaircraft gun, and three triple 25mm A/A mounts atop her hangar.

The most unusual feature was that they each carried three floatplane bombers (and parts for a fourth), a feat never achieved by any other class of submarine. These aircraft folded to fit into the 115-foot cylindrical hangar, which was slightly offset to starboard and opened forward to access the catapult. The huge double hull was formed of parallel cylindrical hulls so that it had a peculiar lazy-eight cross section, and may have inspired the Soviet Typhoon-class built some 40 years later.

Aichi M6A1 Seiran

The aircraft were the Aichi M6A1 Seiran, also carried by the Type AM submarines. Each of these monoplanes could carry one aerial torpedo or a bomb weighing up to 800kg. Powered by the 1,400hp Atsuta 32 engine they had a top speed of 295mph and were credited with a range of 642 nautical miles. The Sen Toku submarines carried four aerial torpedoes, three 800kg bombs, and twelve 250kg bombs to arm these aircraft. These aircraft had their assembly points coated with fluorescent paint to ease assembly in the dark, so four trained men could prepare an aircraft for launch in seven minutes. All three aircraft could be prepared, armed, and launched in 45 minutes.

A restored Seiran airplane is displayed at the National Air and Space Museum in Washington, D.C. Only one was ever recovered and it had been ravaged by weather and souvenir collectors, but the restoration team was able to reconstruct it accurately.

Operational history

For their first mission Vice Admiral Jisaburo Ozawa, Vice Chief of the Navy General Staff, selected Operation PX, a top secret plan to use SubRon One’s ten aircraft to unleash bacteriological warfare on populous areas of the American west coast and Pacific Islands. Infected rats and insects would be dispersed to spread bubonic plague, cholera, dengue fever, typhus and other plagues. General Ishii’s infamous medical laboratory at Harbin, Manchuria, had developed the virulent germ warfare agents and confirmed their lethality by infecting helpless Chinese and Caucasian prisoners.

On March 26th, 1945, this sinister mission was canceled by General Yoshijiro Umezu, Chief of the Army General Staff, who declared that “Germ warfare against the United States would escalate to war against all humanity.” As an alternative the staff considered bombing San Francisco, Panama, Washington or New York, and decided to launch a surprise air strike against the Panama Canal’s Gatun Locks. Destroying these locks would empty Gatun Lake and block the passage of shipping for months.

Before the attack could commence from the Japanese naval base at Maizuru, word reached Japan that the Allies were preparing for an assault on the home islands. The mission was changed to attack the Allied naval base on Ulithi where the invasion was being assembled. Before that could take place, the Emperor announced the surrender of Japan.

I-400 and I-401 therefore returned to Japan and were surrendered to the Allies. After the war, these two were taken to the United States, examined, and finally scuttled in the Pacific in 1946. While there, they received a message that the Soviets were sending an inspection team to examine the submarines. To keep the technology out of the hands of the Soviets, Operation Road’s End was instituted. Most of the submarines were taken to a position designated as Point Deep Six, about 60 km west from Nagasaki and off the island of Goto-Rettō, were packed with charges of C-2 explosive and destroyed. They are today at a depth of 200 meters. I-402 was converted to carry precious fuel to Japan from the East Indies, but never performed such a mission. She was scuttled off Goto Island in 1946. Construction of two further boats of this design, I-404 and I-405, was stopped before completion, although I-404 was 90% complete. A further 13 boats were canceled before construction started.

Four remaining submarines (I 400, I 401, I 201 and I 203 which achieved speeds double those of American submarines), were sailed to Hawaii by U.S. Navy technicians for further inspection. Upon completion of the inspections, the submarines were scuttled in the waters off Kalaeloa near Oahu in Hawaii by torpedoes from the American submarine USS Cabezon on May 31, 1946. The reason for the scuttling is apparently that Russian scientists were again demanding access to the submarines. The wreckage of I 401 was re-discovered by the Pisces submarines deep-sea submarines of the Hawaii Undersea Research Laboratory in March 2005 at a depth of 820 meters.

[Major_Walter_Schmidt]

I-15 class.
Recon plane of the I-25 bombed Oregon.
The bombs caused a forest fire but put out later.

I-26

E14Y “Glen” type zero small recon seaplanne

[windrider]

UH team locates huge Japanese sub

Researchers discover the wreckage of a giant underwater
aircraft carrier scuttled after WWII

Exploring the South Pacific By Burl Burlingame
bburlingame@starbulletin.com
http://starbulletin.com/2005/03/20/news/story1.html
The deep-diving scientists of the University of Hawaii have discovered another monster lurking in the waters off Oahu.

During test dives Thursday, the Hawaii Undersea Research Laboratory’s Pisces submarines found the remains of the Imperial Japanese Navy’s I-401 submarine, a gigantic underwater aircraft carrier built to bomb the Panama Canal.

“We thought it was rocks at first, it was so huge,” said Pisces pilot Terry Kerby. “But the sides of it kept going up and up and up, three and four stories tall. It’s a leviathan down there, a monster.”

It is not the first World War II-era “monster” that the HURL scientists have found. Last year, off Pearl Harbor, they located the wreck of the gigantic seaplane Marshall Mars, one of the largest aircraft built and used as a transport plane by the U.S. Navy. Two years earlier in the same area, the HURL crew also found the wreckage of a Japanese midget sub that was sunk on Dec. 7, 1941.

The latest HURL discovery is from the I-400 “Sensuikan Toku” class of submarines, the largest built prior to the nuclear ballistic missile submarines of the 1960s. They were 400 feet long and 39.3 feet high, could reach a maximum depth of 330 feet, and carry a crew of 144.

HAWAII UNDERSEA RESEARCH LAB
An undersea photo reveals the bridge of the Imperial Japanese Navy’s I-401 submarine. The Hawaii Undersea Research Laboratory’s Pisces submarines discovered the “monster” in waters off Kalaeloa on Thursday.

Each carried three fold-up bombers inside a watertight hangar, plus parts to construct a fourth airplane. The bombers, called Seiran or “Mountain Haze,” could be made ready to fly in a few minutes and had wing floats for return landings. Fully loaded with fuel, the submarines could sail 37,000 miles, one and a half times around the world. Three were captured at the end of the war, as well as a slightly smaller test design called the I-14.

Their first mission was called “Operation PX,” a plan to use the aircraft to drop infected rats and insects with bubonic plague, cholera, dengue fever, typhus and other diseases on American West Coast cities. When the bacteriological bombs could not be prepared in time, the target was changed to the Panama Canal.

I-400 and I-401 were captured at sea a week after the Japanese surrendered in 1945. The commander committed suicide and the huge submarines’ mission was never completed.

I-400, I-401 and I-14 were ordered to sail to Pearl Harbor in late 1945 with an American prize crew, who smuggled Japanese war souvenirs in the aircraft hangars. Also along to be evaluated were I-201 and I-203, two top-secret Imperial Navy submarines that were twice as fast as American designs.

The submarines were greeted with ceremonial brass bands in early 1946, but within a few months it was decided to scuttle the Japanese designs, partly because Russians scientists were demanding access to them. On May 31, 1946, I-401 and the other four top-secret Japanese submarines were sunk by torpedoes from the American submarine USS Cabezon. I-401 was last seen sinking by the stern, vanishing until last week.

“It’s about 820 meters down, off the coast of Barbers Point,” said HURL Acting Director John Wiltshire. “The bow is broken off just forward of the aircraft hangar – it looks like it came apart as it was sinking, as the two pieces aren’t far apart and they’re connected by a debris field.”

According to Pisces VI pilots Kerby and Colin Wolleman, the “debris field” is a twisted landscape of gigantic metal pieces ripped into jagged shreds.

“We had to be very careful approaching that thing,” said Wolleman.

Nearby, the Pisces V crew consisted of John Smith, Max Cremer and Steve Price, and the submersibles helped each other illuminate a path through the wreckage.

“The main hull is sitting upright on the bottom, and it’s in great shape,” said Kerby. “The I-401 numbers are clearly visible on the sides of the conning tower, and the antiaircraft guns are in almost perfect condition.”

With only a few hours available before setting off on a research trip to Samoa, the HURL scientists noted the location of the I-401 for future exploration.

additional links:
http://www.pacerfarm.org/i-400/
http://www.combinedfleet.com/I-400.htm
http://www.afa.org/magazine/march2004/0304sub.asp
http://steelnavy.com/I400.htm

[Major_Walter_Schmidt]

The I-13 class-a kind of a mini I-400

From left: I-400, I-401, I-14

I-14

From left I-400, I-14

I-400 engine room

I-400 float storage compartment.

[Major_Walter_Schmidt]

Notice the US flag. I think the photos were taken after capture.

[Major_Walter_Schmidt]

If you cant see the photos, go here http://www.geocities.jp/i400s/