Yokosuka Naval Shipyard, Japan.
Photographer: U.S. Navy.

Manned by a mixed crew of U.S. Naval officers and Japanese sailors, the mammoth Sen-Toku I-401 cruises near the Yokosuka Naval Shipyard after her name is permanently removed from the roster of the Teikoku Kaigun. 15th of September 1945.

From this day on she will no longer be a submarine of the Imperial Japanese Navy but for a short while will remain with the U.S. Navy to be studied in detail and eventually scuttled near Hawaii to keep her out of the hands of their one-time ally, the Soviet Union.

The scene plays itself out smoothly. No objections are raised. No questions asked. The once-mighty Teikoku Kaigun bereft of authority has virtually no power left to decide the fate of what once was the pride of their submarine fleet.

Not since the day their supreme commander, the emperor Michinomiya Hirohito, announced the unconditional surrender of Japan and brought the juggernaut conflict that was World War II to an abrupt end. Almost a month before the handing over of the submarine.

The largest submarines till the advent of the nuclear powered submarine.

Gradually, with the passage of time. Hirohito’s Japan, an unlikely ally of the first world war, will become a U.S. Protectorate. U.S. military bases will spring up over former Japanese strongholds. And diplomatic ties will once more be forged.

The dissension Hirohito’s rescript will initially sow in the ranks of the Japanese armed forces. Scattered across the Pacific and long tempered by the momentum of war, will in time peter out. As his countrymen will come to terms with events and rise above the chaos of conflicting orders and the very martial honour, that had once made them ready to embrace death over surrender.

Harry S. Truman’s decision to drop the atom bombs will come to be both criticized and defended outside Japan by the Americans, their friends and partners in different continents.

As the cold war will begin to brew between the U.S. and Soviet Union. The world with ambiguous feelings will move forward, towards a new age of cooperation and progress.

Yet all this while, and right up till the introduction of the nuclear powered ballistic submarine. The Sen-Toku I-401, inspite of resting at the bottom of the sea, will remain the undisputed monster of the deep.

A technological marvel of the mid 19th century. And officially the largest submarine to have served in World War II.

Flagship of Tokugata class of submarines.

Spotted and boarded by the USS Segundo. A U.S Baloa class submarine. Returning home from her patrol 100 miles away from Honshu on the 28th of August 1945.

The Sen-Toku I-401 was the flagship of the Tokugata class of submarines. Which by the virtue of their technology, were the most advanced to have sailed the oceans during the time of the intercontinental war.

Produced over a span of three years on the orders of the Commander-in-Chief of the Japanese Imperial Fleet, Admiral Isoroku Yamamoto. The mastermind behind Japan’s victory at Pearl Harbour.

This class of submarines had been specifically conceived to bomb U.S. coastal cities and other targets, undetected by U.S. warships and radar.

Designed for stealth and psychological warfare. Their mission was not to deter or defeat. But delay U.S. forces from launching a full-scale offensive. So as to buy imperial Japan precious time to extend her dominion over the Pacific. Not to mention acquire oil fields.

Underwater aircraft carriers.

Built to launch attack planes like aircraft carriers, the Tokugata class was a testament to the engineering ingenuity of Japanese naval engineers. Who had modified several features of submarine design and ultimately fused two submarine hulls together to make them both operational and buoyant. Albeit not without flaws, which had left them cumbersome to operate, easy to spot from the air and difficult to manoeuvre under the waves.

While out of a proposed ten. Only five were sanctioned to be built. And out of these five, only three were actually built between 1943-45.

These submarines were enormous in size and menacingly lethal. Measuring between 390 and 400 feet in length. They had come with a watertight hanger housing three special attack planes. A deck ramp for the planes to take off. And a crane to lift the planes onto the submarine, once their task was accomplished.

Not to mention, eight torpedo tubes. Anti-aircraft guns. Lighter machine guns. And a 25 mm deck gun. Powerful enough to punch through thick enemy armour.

Furthermore, the hull of this class of submarines was specially coated to reflect radar waves back into the ocean. Which had made them practically invisible to long-range enemy scanners. They were also capable of circumventing the earth one and a half times without stopping to refuel, and remain on patrol for almost 120 days.

The I-401.

Yet, commissioned late in the war, the Tokugata class of submarines, despite their incredible potential, had played absolutely no part in the Pacific conflict. Which leaves their combat capabilities to be determined by theory alone.

Of the three built for service. The I-401 and its sistership the I-400 were the only two to have sailed on a combat mission.

Constructed at the Naval shipyard of Sabeso and registered at the Kure Naval arsenal. The I-401 was launched on the 11th of March 1945.

Among her proposed but never executed missions, was the intended destruction of the Panama Canal and the bombing of the city of San Francisco. In retaliation for the incendiary bombing of Tokyo by the U.S. Airforce on the 9th of March 1945.

Prior to her surrender on the 28th of August 1945. The I-401 and I-400 had been tasked to attack a U.S. fleet of aircraft careers at the Ulithi atoll. They had been ordered to carry out the mission by deploying their three special attack planes known as the Serians.

The Ulithi Atoll was a strategic location in the Western Pacific Ocean. Her capture by U.S forces and the subsequent construction of a naval base had brought the war right to the doorstep of Japan. Thus, had become a threat requiring counter-offensive measures.

Surrender of the I-401.

The I-401 had set sail on her mission on the 23rd of July 1945 from the naval base of Ominato in Honshu. En route, she had come close to being blown apart in friendly fire while navigating through the Tsugaru Strait, which separates the islands of Honshu from Hokkaido.

Before reaching the Ulithi, however, she had received the radio broadcast of Emperor Hirohito’s surrender on the 15th of August 1945. Yet, unsure and with no specific orders to abandon the mission she had continued on her journey.

Till on the 26th of August 1945. Direct orders had made her hoist the black flag of surrender and jettison her planes, torpedoes, secret documents and other weapons for defence.

Thus by the time the USS Segundo had closed in on her, the Sen-Toku I-401 had little onboard to defend herself. Inspite of being built superior to the Segundo in every aspect and a with much greater chances of surviving a naval battle. With only her deck gun left intact at the time. She had allowed five officers of the U.S. Submarine to board her.

Albeit after a brief run for freedom during which time her captain, Lieutenant Commander Nobukiyo Nambu and Squadron commander, Commodore Tatsunosuke Ariizumi had reached upon the mutual decision of having her scuttled to evade capture.

Upon surrender, I-401 had been steered towards the naval base of Yokosuka with her hatches open and chained to prevent her from submerging.

On the 31st of May 1946. Some nine months after her capture. The I-401 had been used as a target ship by the U.S. Navy. With specific orders of having her scuttled. She was sunk with two Mark 18 torpedoes, fired from the USS Cabezon, another Baloa class submarine.

The photo.

While this photo of the I-401 is now archived atWikipedia. The name of the photographer is not mentioned. It may have been taken by a seaman or official from the dock or another sea vessel. Possibly, a U.S. Navy personnel. Clearly visible in the photo is the I-401’s inclined deck ramp and crane for hoisting the Serians.

Interchangeably used the Japanese words Sensuikan Tokugata, Tokugata and Sen-Toku referred to this special class of submarines. Literally translated they stand for Special Submarines or Submarine Special.