Japan’s Underwater Aircraft Carrier / part-one

I-400 Series Super-submarine

Lieutenant Commander Stephen L. Johnson had a problem on his hands; a very large problem. His Balao-class submarine, the Segundo, had just picked up a large radar contact on the surface about 100 miles off Honshu, one of Japan’s home islands, heading south toward Tokyo.  World War II in the Pacific had just ended, and the ensuing cease fire was in its 14th day. The official peace documents would not be signed for several more days.

As Johnson closed on the other vessel, he realized it was a gigantic submarine, so large in fact that it first looked like a surface ship in the darkness. The Americans had nothing that size, so he realized that it had to be a Japanese submarine.

This was the first command for the lanky 29-year-old commander. He and his crew faced the largest and perhaps the most advanced submarine in the world. The Japanese I-401 was longer than a football field and had a surface displacement of 5,233 tons, more than three times the Segundo’s displacement. More troubling though was the sub’s bristling weaponry that included a 5.5-inch gun on her aft deck, three triple-barreled 25mm antiaircraft guns, a single 25mm gun mounted on the bridge, and eight large torpedo tubes in her bow.

During a brief ceremony aboard one of the aircraft carrier submarines, the Japanese naval ensign is lowered and replaced by the Stars and Stripes as the vessel is turned over to the control of the U.S. Navy after Japan’s surrender

The large sub displayed the mandatory black surrender flag, but when the Segundo edged forward, the Japanese vessel moved rapidly into the night. The movement and the continuing display of the Rising Sun flag caused concern.  Johnson’s vessel pursued the craft that eventually slowed down as dawn approached. He brought his bow torpedo tubes to bear on the craft as the two vessels settled into a Mexican standoff.

Johnson and his crew had received permission by now to sink the reluctant Japanese vessel if necessary, but he realized he had a career-boosting and perhaps a technologically promising prize in his sights. Much depended on this untried American submarine captain and his wily opponent in the seas off Japan.

Supersub I-400 series

Little did Johnson know that the Japanese submarine was a part of the I-400 squadron, basically underwater aircraft carriers, and that the I-401 carried Commander Tatsunosuke Ariizumi, developer of the top-secret subs initially designed to strike the U.S. homeland in a series of surprise attacks. Ariizumi was considered the “father of the I-400 series” and a loyal follower of the emperor with years of experience in the Japanese Navy, so surrender was a disgrace he could not endure.

Johnson also had to contend with Lt. Cmdr. Nobukiyo Nambu, skipper of the I-401, who traced his combat experience back to Pearl Harbor. He now commanded the world’s largest submarine designed to carry three state-of-the-art attack planes in a specially built hanger located atop the vessel. These secret Aichi M6A1 planes were initially designed for “a second Pearl Harbor” or another surprise attack, possibly even against New York City or Washington, D.C. The I-400 series submarines were themselves full of technological surprises.  They were capable of traveling around the world one and a half times without refueling, had a top surface speed of 19 knots (or nearly 22 miles per hour), and could remain on patrol for four months, twice as long as the Segundo.

Neither Nambu nor Commander Ariizumi readily accepted the emperor’s surrender statement when it was broadcast on August 15. The subsequent communiqués from Tokyo were exceptionally confusing, especially Order 114, which confirmed that peace had been declared – but that all submarines were to “execute predetermined missions and attack the enemy if discovered.”

Admiral Isoroku Yamamoto

It was Admiral Isoroku Yamamoto, commander of Japan’s Combined Fleet and developer of the Pearl Harbor attack, who called for the construction of the I-400 series some three weeks after Pearl Harbor.  Once Japan was committed to war, he believed that submarine aircraft carriers dropping bombs “like rain” over major U.S. cities would surely cause the American people to “lose their will to fight.” A second surprise attack with even more to come would prove psychologically devastating to the Americans.

To be continued…

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Military Humor-

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Farewell Salutes – 

William K. Beers – Lewistown, PA; US Army, Vietnam, 101st Airborne & 17th Artillery

George E. Bernard (100) – Burlington, VT; US Navy, WWII, ETO, Seaman 2nd Class, LCT Rocket # 373

Charlotte Clark – Laconia, NH; Civilian, WWII, Scott & Williams Aircraft parts

Milton Cronk (100) – Iowa City, IA; USMC, WWII, PTO, Marines Raiders, Purple Heart

Frank Daniels – Watertown, MA; US Navy, WWII, PTO, gunner, Seaman 1st Class

R. James Giguere – St. Paul, MN; US Army Air Corps, WWII, ETO, B-17 “Miss Lace” bull turret gunner

William C. Jones (100) – Fort Smith, AR; US Navy, WWII

Ruth (Lias) Lowery (100) – Akron, OH; Civilian, WWII, B-17 production

Johnnie Mullenix – Unionville, MO; US Navy, WWII, PTO

Richard Shaug – Cambria, CA; US Army, Korea, HQ Co/187th RCT

Twila Wellsfry – Chico, CA; Civilian, WWII, bookkeeper, Mares Island shipyard

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