By Henry Sakaida

kaiten kamikaze suicide torpedo submarine

From the cover of the paperback book titled Suicide Submarine! by Yutaka Yokota with Joseph D. Harrington. The human torpedo program was a dismal failure.

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 Navy officers in 1944. The designers were Lts Hiroshi Kuroki and Sekio Nishina. The pair were killed while testing them. During development and training, the craft was known as the “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 gyrocompass 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 kamikaze suicide torpedo submarine

Kaiten on display at the Yasukuni Shrine Museum in Tokyo. They were credited with sinking the USS Mississinewa, a fleet oiler; the destroyer USS Underhill (DD-682), and a 236-ton LCI-600, a small infantry landing craft (3 crewmen killed). Photo credit: Mori/Photos Aug 2008 Tokyo.


kaiten kamikaze suicide torpedo submarine

Basic structure of the human torpedo. It had a range of 42 nautical miles, with a top speed of 30 knots. The Japanese standard “Long Lance” torpedo fired from a submarine was a far superior weapon than the Kaiten.

As a high school kid, I read about the Japanese human torpedo in a paperback book titled Suicide Submarine! It was about a surviving kaiten pilot named Yutaka Yokota. He co-authored the book with American writer Joseph D. Harrington, a retired Navy chief journalist, in 1962.


kaiten kamikaze suicide torpedo submarine

Petty Officer 1st Class Yutaka Yokota. Trained as a fighter pilot, he volunteered for the top secret Kaiten program in the summer of 1944.


kaiten kamikaze suicide torpedo submarine

Yutaka Yokota, far left, with his group just before their sortie in April 1945. He survived because of mechanical problems to his assigned mount.

Back around 1989, I met a former sailor in the US Navy named James B. Roberts, of Lakewood, CA through his son Don. He was excited to tell me about his ship’s battle against a human torpedo! I had talked with numerous American survivors of Kamikaze attacks, but this was the first and only time I would hear about a human torpedo attack!

The fateful day was 28 June 1945. Torpedoman 2nd Class Jim Roberts, 23 years old, was serving aboard the destroyer Sproston (DD-577). The Fletcher-class destroyer was making its way back to the US for overhaul when it received a SOS from the USS Antares (AKS-3), an armed cargo ship. It reported being attacked by a Japanese submarine between Saipan and Eniwetok in the Marshall Islands on its way to Pearl Harbor.


Torpedoman 2nd Class James B. Roberts


USS Sproston (DD-577). It was launched in August 1942 and did anti-submarine duties in the Aleutians, then fought in the Philippines and around Okinawa. She served in the Korean and Vietnam Wars and was decommissioned in 1968.

The freighter believed that it had successfully dodged a torpedo from a Japanese submarine (identified postwar as the I-36). However, the sub never fired one. The skipper, LCdr Tetsuaki Sugamasa, opted to use a kaiten piloted by Lt(jg) Nobu Ikeguchi. Gunners aboard the ship spotted his periscope and fired on it until it sank.

“We were approaching the Marshall Islands on our home voyage to San Francisco when my ship received a distress call from a transport ship,” recalled Roberts. “They were being stalked by a Japanese submarine and were firing on it as our captain swung the ship around to give assistance.”

When the Sproston arrived in the combat zone, her observers immediately spotted the periscope of the I-36. LCdr Sugamasa was so focused on monitoring the attack of his kaiten, he failed to detect the approach of the destroyer. This nearly proved fatal. When Sugamasa swung his periscope around to scan the horizon, he was horrified to see a large black shape filling his view!

“Stand by to ram!” ordered Cdr Robert J. Esslinger on the bridge. “I was on the stern and braced myself for that awful collision,” recalled Roberts. “We were getting up to 35 knots (40mph) maximum speed. I knew that there was going to be serious damage, to the both of us!”

Cdr Robert J. Esslinger was the skipper aboard the Sproston. He had a distinguished career and retired as a rear admiral.

It was straight out of Hollywood. “Emergency dive, take her down to 125!” yelled Sugamasa.  The crew bolted into action. Just as the 3,000+ ton Sproston reached the point of impact, the submarine slid serenely underneath the destroyer’s bow. The men on the bridge of the destroyer looked down to see the long black shape of the I-36 directly underneath them! They had missed by feet!

“We had originally set the depth charges for 50 feet,” said Roberts. “Now, there was no time to reset it. We rolled the 600 pound ‘ash cans’ off the stern and shot the 300 pounders from the K-guns into the air. We busted our tails to get that sub!”

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.”

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 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.

kaiten kamikaze suicide torpedo submarine

Captured Kaiten can be seen at the USS Bowfin Museum in Pearl Harbor.

kaiten kamikaze suicide torpedo submarine


kaiten kamikaze suicide torpedo submarine


kaiten kamikaze suicide torpedo submarine

This model of the submarine I-153 shows how the kaiten was arranged on a large fleet submarine. Two were placed in the front and 3 were loaded on the back.


kaiten kamikaze suicide torpedo submarine

Kaiten pilots entered their craft through a small tube connected to the submarine. Once inside, they were sealed shut. The kaiten and the submarine did not have contact after separation. The submarine could only observe through its periscope and sonar. Model courtesy of Steve Hayama.


For Further Reading Check Out:

Kaiten: Japan’s Secret Manned Suicide Submarine and the First American Ship It Sank in WWII

Suicide Submarine! The Story of Japan’s Submarine “Kamikaze” of Manned Torpedoes!

For Books by Henry Sakaida Check Out:

Heroes of the Soviet Union 1941–45

Heroines of the Soviet Union 1941–45

I-400: Japan’s Secret Aircraft Carrying Strike Submarine, Objective Panama Canal

Genda’s Blade: Japan’s Squadron of Aces: 343 Kokutai

Aces of the Rising Sun 1937–1945

B-29 Hunters of the JAAF


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