Japan’s Underwater Aircraft Carriers – conclusion

American naval personnel inspect the hangar of a Japanese submarine aircraft carrier. The hangar tube was sealed by a two-inch-thick rubber gasket, and the hatch could be opened hydraulically from inside

By early 1945, the Japanese Navy had only 20 modern submarines left, including those in the Sen-toku squadron. Problems arose as the two available I-400 subs began test launching their Sieran planes. Each submarine was required to surface and get its three planes unlimbered and aloft within 30 minutes, but actual training showed that it took some 45 minutes.

Because of an increasing sense of urgency, the Japanese further modified their plans. A torpedo attack was ruled out because the pilots had not yet acquired the requisite skills. It was decided that each of the 10 planes designated for the Panama Canal mission would carry one 1,760-pound bomb, the largest in the Navy’s arsenal and similar to the one that sank the battleship USS Arizona at Pearl Harbor

The departure date was set for mid-June.  The Seiran pilots made practice bombing runs in Nanao Bay against a full-sized replica of the Gatun gates.

The fall of Iwo Jima in March 1945 and the American attack on Okinawa increased the angst among the Japanese planners as the Americans closed in on the home islands. The war had leaped ahead of the planners, and the slated attack on the Panama Canal was canceled. As noted, there were discussions about possibly using the planes in a surprise attack on San Francisco or Los Angles, but those, too, were put aside in favor of a plan to attack enemy carriers at Ulithi, a large staging area near the island of Truk in the Carolines that was used by the Americans.

Mail call on Ulithi, 1945

The two large subs were to proceed toward Ulithi independently for safety and then rendezvous near the target and launch the attack in mid-August. The I-13 never made it to Truk and was correctly presumed lost. The I-14 arrived at Truk on August 4, and its planes flew over Ulithi the following day.

Shortly thereafter word reached the submarines that an atomic bomb had destroyed Hiroshima, and on August 15 the Japanese seamen heard the broadcast from the emperor asking his warriors to lay down their arms. Subsequent orders from the homeland were confusing, with one commanding all submarine captains to execute their predetermined missions. On August 16, the underwater aircraft carriers received explicit orders that their planned attack on Ulithi had been canceled just hours before the I-401 was to launch its planes. The subs were ordered to Kure, and the I-401 turned course toward its fateful encounter with Lt. Cmdr. Johnson and the Segundo.

The Japanese eventually surrendered the I-401 and the other two remaining underwater aircraft carriers. Commander Ariizumi, the developer of the top secret subs, took his own life aboard the I-401 and was quietly buried at sea by the crew. Before encountering the Americans, Nambu had meticulously followed orders from Japan to raise the black flag of surrender and dispose of the vessel’s weapons, including the planes that were catapulted into the sea. Logbooks, code-books, and the like were loaded into weighted sacks and tossed overboard. The torpedoes were jettisoned, with one causing alarm as it circled back toward the large submarine before disappearing harmlessly into the depths.

The Japanese aircraft carrier submarines I-14, I-400, and I-401 are shown in Tokyo Bay at the end of the war. The submarines were destined to be sunk in Hawaiian waters during U.S. Navy torpedo tests.

The three submarines drew considerable attention when they made it back to Tokyo Bay.  Many Americans initially believed the large hangars atop the subs had been designed to haul supplies to troops on distant islands despite the clearly observed catapults. The Americans did receive some assistance from the Japanese crews as they tried to comprehend the purpose of the extraordinary submarines, and by the end of September the Americans had taken the submarines out for cruises. However, none was taken underwater.

The submarines were then taken to Hawaii for further study. The U.S. Navy gleaned what it could from them, and then all three were deliberately sunk by early June 1946 to keep them away from the prying eyes of the inquisitive Soviets.

One of the Seirans did make it to the United States after the war and was eventually restored at an estimated cost of $1 million. It is now on display at the Smithsonian Air and Space Museum. Although the U.S. Navy was somewhat dismissive of the massive submarines, it did take a keen interest in the sound-protective coatings used on the vessels.

There is little doubt that the I-400s were the strategic predecessors to today’s ballistic submarines, especially to the Regulus missile program begun about a decade after World War II that carried nuclear warheads inside waterproof deck hangars. In short, Yamamoto’s plan lived on with “new and improved” versions that helped the United States win the Cold War.

This has been condensed from: Phil Zimmer is a former newspaper reporter and a U.S. Army veteran. He writes on World War II topics from Jamestown, New York.

The wreck of IJN !-401 was located in March 2005.

Click on images to enlarge.

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Military Humor –

 

 

 

 

 

 

 

 

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Farewell Salutes – 

Ronald D. Brown – Pembroke, KY; US Army, Korea, 187th RCT

They stand on the line for us.

Richard E. Cole -(103) – Comfort, TX; US Army Air Corps, WWII, Doolittle’s co-pilot, Lt. Colonel (Ret. 26 y.)

Robert Hendriks – Locust Valley, NY; USMC, Afghanistan, Cpl., 25th Marine Reg./4th Marine Division, KIA

Benjamin Hines – York, PA; USMC, Afghanistan, Sgt., 25th Marine Reg./4th Marine Division, KIA

Delmar Jones – Sesser, IL; US Army, WWII

Venizelos Lagos – Culpepper, VA; US Coast Guard, WWII

Virgil Patterson – FL; US Navy, WWII, PTO

Christopher Slutman – Newark, DE; USMC, Afghanistan, SSgt., 25th Marine Reg./4th Marine Division, KIA

Ly Tong – VIET; South Vietnam Air Force, Black Eagle Fighter Squadron, pilot, POW

Bryan Whitmer – Grand Rapids, OH; US Army Air Corps, WWII, PTO, HQS/457 Artillery/11th Airborne Division