War History Online proudly presents this Guest Piece from Hans Wiesman
In this DAKOTA HUNTER Blog, you can read about the Japanese Monster Aircraft Carrier Submarines, built initially for raiding the US Coasts.
The Japanese Navy under the visionary Admiral Yamamoto (architect of the Pearl Harbor Assault in December 1941) developed a plan for a fleet of huge Subs that each carried 3 Hi-Tech attack/ bombers inside a tubular hangar, that was mounted on a double tubular fuselage. The novel design of the I-400 series (built in December 1944) gave stability with 2 hulls welded next to each other and made up for the largest Submarine ever built until the 1960’s nuclear subs came out.
Overall length was almost 400 whopping feet (122 m) and an armament of a huge 140 mm canon plus 4 power packs with 25 mm AA guns and special torpedo’s inside. The Monster Subs were weighing 5,700 tons, carrying a crew of 200 and possessing a range of over 50,000 miles, with weapons and 3 aircraft designed to become the first Submarine fit for an offensive strike on the US mainland targets on West & East Coast!
The real surprise novel was on top of the double hull, a spectacular hangar with inside 3 Aichi-M6 Seiran aircraft that could each carry an 1850 lbs. bomb over 1,000 miles. From a long launch ramp on the front deck of the sub, a steam catapult was used to shoot the aircraft airborne and after landing on their floats, a foldable crane was used to hoist the aircraft back on board. Five of the Monster Subs were built, but only three were launched. One made a trip around the Horn of Africa to Germany and another one was converted as a sub-tanker. The I-400 series submarine had a number of advanced features like radar and the by Germans invented snorkel for extended underwater cruising on the Diesel engines, allowing the batteries to be charged. But most amazingly also stealth technology: energy absorbing skin with a rubberized coating that would help the submarine remain undetected by sonar equipment of the Allied Sub hunters.
The original order of 18 such I-400 series Subs was slashed to 9 after Admiral Yamamoto got killed by a US Interception force on the way to the Solomon Islands on April 18, 1943. The Allies broke the secret Japanese Navy codes and shot down his plane in an ambush. With the inspirational mind and power of the Master gone, the Monster Submarine program soon started to lag behind the fast developments in the Pacific War and a tragic career of missed opportunities followed for what was potentially the most lethal weapon the Japanese had to threaten the dominant US Navy in the Pacific.
In December 1944 the first of the series, I-400 was commissioned, soon followed by I-401. Their original plan to terrorize the US West Coast cities failed as the impact of only 2 subs with 6 planes would not be sufficient to create large-scale havoc and becoming a real menace for the USA. This plan was not fully abandoned, instead, the Japanese developed a similar plan but with the use of Biological weapons to attack large cities and spread bacterial diseases, the killer bug they had developed in China since the late 1930s. In this blog, you can read how the USA escaped from this ordeal.
Once inside, the huge watertight front door was locked with a clamp and the ship could sail to any place over the globe and return without a single stop for refueling. Again a new plan emerged: Attacking with the 2 giant subs the Panama Canal and destroy the Gatun Locks with a Kamikaze attack of the 6 Aichi Bombers. The destruction of a water lock door could effectively block the ship’s passage for months. But again, the plan had to be abandoned due to the strong progress of the US Navy towards the Japanese homeland in early 1945. It was all hands on deck for helping the Japanese Navy in its agony.
In their final attempt to let the subs do what they were built for, the I-400 and I-401 were sent for a desperate assault hoping to turn the tide for the Imperial Japanese Forces. The much feared US Aircraft carriers were all gathered near the small Ulithi Atoll (East of Philippines) in preparation for the last big naval attack. Their presence lured the Japanese Monster subs. But again, the events ran faster than the boats could sail. On their way to the Atoll, the Atomic bombs fell on 6 and 9 August. Hence, on 15 Aug.1945, both subs received the news of the Japanese surrender: they were ordered to give themselves over to the US Navy.
Their bombers had been pushed overboard to avoid capture, but in Japan, the US Army later found one surviving example and did extensive testing. That aircraft is now on display at the Smithsonian Institution in its Aviation Museum near Dulles International Airport, Washington DC.
After their arrival in Tokyo, the US Navy understood the importance of this “catch” and obviously tried to keep them away from other nation’s spy eyes. The Monster Subs were soon sailed to Oahu/ Hawaii and were docked for an in-depth inspection of their very advanced technology. The Russians claimed the subs as war booty, but evidently, the US Navy was not very willing to hand over those much-wanted ships in the light of the looming Cold War in 1946.
They took the captured Japanese Monster subs to a deep sea southwest of Oahu and sunk them by torpedos or scuttled them. The I-400 was sunk on May 31, 1946, and the I-401 on June 4, 1946. With that ‘accident”, the Monster subs never showed up at the rendezvous with the Russians! “Hey Joseph, so sorry, we must have lost them at the high seas we encountered while they were being towed for a handover to you guys. And no, we can’t remember where that happened.”
After the occupation of Japan, 24 operational submarines of the Japanese Imperial Navy were sunk off Goto Island near Sasebo, including the I-58, which had sunk the USS Indianapolis. But the I-400 and I-401, the 400-foot I-14c, and two fast attack Subs I-201 and I-203 were to be taken to Hawaii for further inspection. For more information of the I-58 that sunk the USS Arizona, see my earlier blog about the Dumbo Catalina that saved 56 sailors in that largest ship wrecking disaster since Pearl Harbor. Click here Dumbo PBY Catalina saves USS Indianapolis sailors
In the year 2013, the buckled I-400 Monster Sub was discovered, resting on the ocean floor at 2,300 feet depth in the Pacific Ocean off the southwest coast of Oahu. (see picture below). The once ultra advanced submarine was discovered by Hawaii Undersea Research Laboratory explorer Terry Kerby and colleagues from the National Oceanic and Atmospheric Administration and the University of Hawaii at Manoa’s School of Ocean and Earth Science and Technology.
Read and see more about the torpedoing and discovery of the I-400. There is a film with authentic footage of both subs, this is 52 mins video but better than any Hollywood production! Please view it here and enjoy!
If you are interested to read more of my stories about War History and Vintage Aviation, please come to my Book & Blog site atwww.dc3dakotahunter.com
My first book The Dakota Hunter is a non-fiction report about my 20+ years in search of the legendary DC-3 at the last Frontiers. Fascinating stories of what I experienced in the forgotten Jungles of the Amazon, the remote Altiplano of Bolivia, the swamps of Madagascar and the desolate mountains of the Yukon.
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