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Japanese Kaiten Torpedo

Kaiten Type-1 Yushukan on display in Tokyo

IJN Navy officers in 1944, were the designers, Lts Hiroshi Kuroki and Sekio Nishina. The pair were killed while testing the weapons.

In the desperate final year of WWII in the Pacific, very few people on both sides knew of the existence of the Japanese kaiten human torpedo. It was a top secret weapon developed by two “Circle 6 metal fitting” and only a few in the Imperial Navy knew what it really was.

The kaiten was the underwater equivalent of the Kamikaze suicide plane. Although the human torpedo pilots did not die in a blaze of glory as their air force counterparts, they all believed in their cause and there was no shortage of volunteers for the top secret program.

The kaiten was powered by a Type 93 “Long Lance” torpedo engine fitted to a long tubular body. The engine was oxygen-powered and had a maximum speed of 30 knots (34.5 mph). The 54-foot weapon packed a 1550 kg (3,420 pound) warhead and was controlled and guided by a human operator. There was a tiny pilot’s compartment which had a periscope and a gyro-compass to guide him to the target. Once launched, the weapon could not be recovered. There was a self-destruct button if the pilot failed to hit his target.

Kaiten Type-10 schematic

To sink a submarine was very difficult. The killing radius of the exploding depth charge, depending on various circumstances such as depth, payload, and strength of the target’s hull, was around 10 to 13 feet. From 26 to 33 feet, serious damage could be inflicted. It took a lucky hit to sink a submarine; most were sunk after being battered continuously until they lost power or air. The US Navy had perfected anti-submarine warfare using high tech equipment and teams of destroyers and destroyer escorts. The danger point for the submariners was about 12 hours without fresh air. By forcing the sub to surface  or preventing it from surfacing for air, its destruction was assured.

Petty Officer Yutaka Yokota, a kaiten pilot on the I-36, recalled: “Then came the depth charges. They felt like a giant pile driver smashing into the side of the I-36. She shook and swerved, throwing me to my knees. The wardroom sofa leaped fully two feet above the deck and toppled over on its side. Every light that I could see went out, and only about half of them came on again.”

USS Sproston

The I-36 was taking a severe beating and there was nothing she could do. It had launched one kaiten, but it still had 5 more strapped to the deck. Sugamasa wanted to dive down to 325 feet, but his cargo prevented him from doing so. To dive deeper meant that he would destroy the kaitens due to heavy underwater pressure.
Oil and debris came bubbling to the surface, but Cdr. Esslinger on the USS Sproston wasn’t falling for that old submariner’s trick. The crew smelled blood in the water and increased their resolve. They had knocked down several Japanese planes, but wanted to add a submarine to their  tally.

LCdr. Sugamasa was running out of options. Then Ensign Minoru Kuge rushed into the con and volunteered to man his kaiten and counter attack. All of the electric rudders on the small crafts were damaged, but they could be steered manually. Petty Officer Hidemasa Yanagiya also insisted to sortie. Sugamasa knew that a counter-attack had little chance of success. These two brave men were going to sacrifice themselves to lure the destroyer away from their submarine so that she could escape.

Yokota’s kaiten was badly damaged. He had sortied twice before, only to be thwarted by mechanical failures in the temperamental kaiten. He was confident that the third sortie would be the charm. Now a bystander, he stood by clutching a vial of cyanide and thought “Once they made their direct hit and water came rushing into our hull, I was going to swallow the container’s contents. I could not bear to think of death by drowning or suffocation.”


Kuge and Yanagiya quickly boarded their kaiten through a tight hatch and were sealed shut. The engines started, the clamps were released, and the two kaitens whirled their way toward the surface. The skipper and his sonarmen listened intently through their earphones. Fifteen minutes later, the first contact was made.
Sproston had spotted a kaiten and made a run towards it. The conning tower and periscope were clearly visible at quite a distance.Then the 5-inch guns opened up. Sugamasa and his sonarmen heard faint explosions. “We made a direct hit!” recalled Roberts. “I saw the small black conning tower go sailing off into the air!” There was wild jubilation! The Sproston had scored.

Down below in the I-36, they later heard a gigantic boom; a kaiten had exploded. But which one, Kuge or Yanagiya? Believing that it had scored a kill, they cheered. But they were wrong. The depth charges kept coming. From noon until night, the destroyer pounded the submarine until their inventory of depth charges was depleted. Finally, the destroyer retired from the scene. The I-36 limped back into port like a beaten dog on 6 July 1945. For Yutaka Yokota, he was unsuccessfully lucky, for he lived to tell about it.


Through the diligent efforts of Don Roberts (Jim’s son), the connection between the Sproston and the I-36 was made. Don located Yutaka Yokota in Tokyo and exchanged letters. The USS Sproston Association invited the former kaiten pilot to their reunion in Orlando, Florida in September 1990. Yokota could not attend due to ill health. The old sailors were looking forward to meeting Yokota at the 1992 reunion in Chicago, but were saddened to learn that he had passed away on 16 March 1991 of cancer at age 65.

Jim Roberts had sent a letter to Yokota prior to his passing. In his letter, Jim wrote: “We tried our best to sink you. But I am glad that we did not do so.” This letter was read at Yokota’s funeral wake. About a hundred of Yokota’s comrades, many of them from the kaiten program and the submarine service, attended his funeral. “I wish we could have met,” sighed Jim. “We had so much to talk about.”
Jim Roberts passed away at his home in Lakewood, CA in 2004.

Click on images to enlarge.

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Military Humor – 

 

 

 

 

 

 

 

 

 

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Farewell Salutes – 

Glen Azevedo – Riverside, RI; US Coast Guard, Vietnam, Chief Warrant Officer

James Barrett – Palmerston North, NZ; RNZ Army # 33572, WWII, Warrant Officer 1st Class

James Bates – Kimmins, TN; US Army, WWII, ETO, POW / Korea, (Ret. 30 y.), Silver Star, Bronze Stars

William Danner – Elwood, IN; US Army, WWII, 104th Infantry Division, Chief Warrant Officer2 (Ret. 25 y.)

Robert Fitzgerald – Charles City, IA; US Navy, WWII

Melvin Liederman – Hallendale, FL; US Army, WWII, ETO

Guy Nightingale – Corning, KS; US Navy, WWII

Richard Pride – Hampton, VA; US Army, WWII, Major / NASA engineer

Joseph Rosario – Morristown, NJ; USMC

Fred Segal – Detroit, MI; US Navy, Lt., Taurus Missile System

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Research for Jeff S.

Pictures are larger than shown here.

511th area is indicated within the red circle

The 511th traveled west to Lipa

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