The recent successes of Ukrainian “suicide drone boats” against ships of the Russian Black Sea Fleet remind us of earlier fast-attack boats designed to target warships — the Japanese “Shinyo” suicide boats of World War II.
In late 1944, as the empire of the Rising Sun started to shrink, the Japanese began to take drastic measures to defend their island bases. In an effort to turn back the Allied invasion fleets, the Divine Wind concept of “one plane — one ship” introduced the term “Kamikaze” into the military lexicon of the era. Soon after, suicide methods were introduced by the Japanese infantry, most notably in anti-tank defense.
The Shinyo were intended to strike shipping in the crowded anchorages off the coasts of invasion beaches. Image: NARA
To combat American landing craft and other warships operating close to the invasion beaches, the Japanese Navy brought forth a number of fast-moving, explosive motorboats. The Shinyo joined in the barrage of suicide attackers, with each boat piloted by one man on a one-way mission.
The crowded anchorages just offshore the landing beaches offered a target-rich environment for the Shinyo pilots. Once they were among the many transport ships there were few defenses specifically prepared to stop them. The U.S. Navy first encountered the explosive boats during the invasion of the Philippines.
A small fleet of Shinyo suicide craft, seen in a harbor in the Japanese home islands after WWII. Image: NARA
The following report describes the new danger from small Japanese craft:
A Japanese captured in the Manila Bay area stated that at the time of our landing there were 100 suicide boats around the shores of Corregidor Island. These boats were kept in tunnels at various points around the island (from which they could be launched by means of dollies) or concealed above ground, particularly between San Jose Point and Camp Point.
U.S. servicemen located a camouflaged Shinyo-class boat near the beach on Okinawa. Image: NARA
The boats were described as 20 feet long, having a speed of 20 knots and being manned by a single naval volunteer. Although they mounted no guns, the boats carried a 250 kilo (551 lbs) charge in the bow which could be detonated either by key or on impact. It is considered probable that boats attacking our shipping around Mariveles last week came from Corregidor. As our advances on Corregidor continue, some of these boats as may still be serviceable will probably attempt to retire to CANDAPAT Swamp (the only sector of the Manila Bay area not immediately threatened by our ground forces) until targets in the form of our large vessels enter the inner harbor.
SWPA Daily Summary, February 20, 1945
Shinyo — Identified and Described
Navy units soon learned how to respond to the new threat. “Small boat patrols” were quickly organized with available units, night watches were alerted, and radar operators were given instructions on what to watch for. Even so, the small Shinyo-class motorboats had certain advantages as they stalked USN warships at night.
A Japanese Shinyo explosive motorboat captured on Okinawa by U.S. Marines during World War II. The trolley used to launch the boat is also seen in this photo. Image: NARA
The destroyer USS Charles J. Badger (DD-657) was damaged by a Shinyo on May 19, 1945, and the ship’s log succinctly describes the difficulties in locating the small enemy boats:
Detection is difficult for the following reasons:
Visual: Low in water, well camouflaged, dark.
Radar: Low in water, flimsy wood construction.
Sound: Muffled, idling speed approach.
A 1945 U.S. Navy Report provided a concise definition of the Shinyo craft:
SHINYO “SPECIAL ATTACK BOAT”
General: SHINYO, applied to Japanese naval craft, signified a small boat which utilized the explosive charge carried in its bow by ramming the side of the intended victim.
SHINYO boats were manned by middle school boys about 15 to 16 years old. It is reported that an ample supply of volunteer pilots was obtained because of the special privileges, early responsibility, and the promise of a posthumous monetary reward to the volunteer’s parents.
SHINYO boats were collected in special attack basins along the coast, carried on mother ships, and even stored in bomb-proof cases equipped with dollies and tracks for launching. Plans for the carrier Junyo were discovered which showed the flight deck and both hangar decks completely covered with SHINYO boats.
The cockpit of a captured Japanese Shinyo. A 120mm rocket is mounted on the right side of the boat, while the left mount is empty. Image: NARA
Special booms lifted off two SHINYO boats at a time and special fenders separated them while being lowered. It seems probable that the Japanese intended to transport a large number of SHINYO at one time to another base and that they did not intend to fight an engagement with the “Junyo-Shinyo” combination.
The SHINYO attack procedure was to crash the side of the target. The rudder could be lashed, allowing the pilot to jump overboard just before impact, though it was expected that each pilot would make sure of a good hit by riding his craft to a glorious death.
The only two types of Shinyo used in combat were relatively slow, 23 and 25 knots; hence the SHINYO program involved a constant struggle to develop an extra high-speed boat for efficient daylight strikes.
Shinyo’s Suicide Mechanics
The Shinyo was a simple craft, designed to carry an explosive charge (about 600 lbs. of Type 98 explosive) to attack other surface vessels in a suicide attack. The cockpit contained the steering wheel, magnetic compass, engine controls, and controls for the bow explosive charge.
The Shinyo saw significant service during the Okinawa campaign. Fortunately, this one was captured before it could be used against American forces. Image: NARA
The Type 1, Model 1, was powered by a standard Toyota KC 6-cylinder automobile engine, delivering a somewhat disappointing speed of 23 knots. The explosive charge in the bow contained an electric detonator; as well as a manual, pull-type firing device.
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The charge could be fired by three methods: (1) electrically on impact, (2) electrically by a manual switch, and (3) by pulling the pull igniter. For the bow contact switch, a steel strip with several “spikes” on it was separated from another steel plate by a rubber strip.
This captured Shinyo boat was hiding inside its beachside bunker when it was found on Okinawa during World War II. Image: NARA
Bow impact would force the spikes through the rubber, close the electric circuit, and fire the charge. The 600-lb. charge would split open most merchant ships and lightly constructed warships like destroyers and minesweepers. Two 120mm rockets were mounted on simple wood launching troughs on either rear quarter, intended to be fired at the target ship to suppress its gunners on the Shinyo’s attack run.
Shinyo Victims
January 10, 1945: The USS LCI(G)-365 (Landing Craft Infantry/Gunboat), USS LCI(M)-974 (Landing Craft Infantry/Mortar) were sunk, and the transport USS War Hawk was damaged in Lingayen Gulf, Luzon, Philippines.
January 31, 1945: The sub chaser USS PC-1129 sunk off Nasugbu, Luzon, Philippines.
February 16, 1945: The USS LCS(L)-7 (Landing Craft Support/Large), LCS(L)-26, and LCS(L)-49 were sunk off Mariveles, in the Corregidor Channel, Luzon.
April 4, 1945: The USS LCI(G)-82 (Landing Craft Infantry/Gunboat) and USS LSM-12 (Landing Ship/Medium) were sunk off Okinawa.
April 9, 1945: The destroyer USS Charles J. Badger (DD-657) was damaged off Okinawa.
April 27, 1945: The destroyer USS Hutchins (DD-476) was badly damaged in Buckner Bay, Okinawa.
May 4, 1945: The cargo ship USS Carina (AK-74) was damaged in Buckner Bay, Okinawa.
U.S. Countermeasures
I searched through a wide selection of U.S. Navy reports to identify details about Shinyo attacks. The ships and sailors were quick to react and develop new tactics to counter the small boat threat. Interestingly, various small arms, including the .45 caliber Thompson submachine gun, the venerable M1903 rifle, and the .30 caliber Browning M1919 MG became effective countermeasures when it was found that 20mm and 40mm AA guns could not be depressed enough to hit the small surface craft.
One of the prime Shinyo targets was the U.S. Navy’s Landing Craft, Tank (LCT). This one was photographed off the coast of Okinawa during the Second World War. Image: NARA
The following is a comment from the USS LCI(G) 659 Anti-Small Craft Screening Station, off the coast of Okinawa, near the town of Naha.
“On 16 April 1945, this ship contacted and sank two Japanese small suicide craft. The first was detected by a cruiser initially and shortly afterwards by this vessel. We approached to about 300 yards of the boat and then illuminated the target and opened fire with two 20mm’s and one .50 caliber machine gun. The boat, underway and proceeding at a slow but increasing speed in the opposite direction, caught fire and a few seconds later exploded and sank, the explosive charges it carried presumably causing the explosion.
A Shinyo-class motorboat is stranded on the beach during the invasion of Okinawa in World War II. A first-generation U.S. Marine Corps LVT (aka: Amtrac) rests in the background. Image: NARA
“The second boat was contacted by radar; we closed the target and when about 250 yards from it, illuminated it and opened fire. Three 20mm’s and two .50 caliber machine guns riddled the boat, but it did not catch fire or explode as the previous one had, and at first it attempted to keep out of our lights. It suddenly disappeared altogether from sight and from the radar screen and was assumed to have sunk as no further trace of it was found.”
It was learned that small arms made a big difference. Note the following comments:
“50-caliber guns were particularly effective because of their ability to depress at very close range.”
“O.O.D. challenged small boat and upon receiving no answer and as small boat was rapidly approaching stern, opened fire with a .45 caliber machine gun. Small boat swerved and headed up port side of ship, in close. Unable to bring the 40mm or 20mm to bear on target. As small boat proceeded up port side, two explosions occurred on port quarter which rocked the ship violently. As small boat passed bow, Arthur Boyd, GM2c USNR, emptied a clip from a .45 caliber machine gun into small boat before it disappeared from sight into the dark. Results of firing not observed due to darkness.”
The following is a comment from the US LCI(G) 82 on the night of April 3-4, 1945 off Okinawa.
A Shinyo motorboat was found outside of its cave lair when the area was taken by U.S. Marines on Okinawa. Rocket launchers are seen mounted aft. Image: NARA
“The boat approached rapidly, turned, and crashed into the ship on the port side just forward of the conning tower. A double explosion resulted, tearing a large hole in the side of the ship. The explosion knocked out all the ship’s lights and ship immediately heeled to starboard. Number two and three compartments started to fill with water and within five minutes of the attack, flames were shooting out of the number two compartment, through the hatch and through holes in the deck. The life rafts were launched and loaded with the wounded. The fire enveloped the forward section of the ship and started to spread aft. Ammunition began to explode forward and the ship was abandoned approximately fifteen minutes after the attack.”
Following is a comment USS Density, AM-218 Admirable class minesweeper off Okinawa May 4, 1945.
“The location of the .30 caliber machine gun on the lip of the sponson, on the open bridge, is a good one. It is limited in its training arc but can be depressed considerably lower than any of the 20mm or 40mm. A lesson learned is hereafter hand grenades and a Tommy gun will be available to Repair Party #2 on the fantail.”
A good condition example of the Shinyo preserved on Okinawa after the Second World War. Image: NARA
Conclusion
Ultimately, like most of Japan’s desperate measures near the end of the war, the Shinyo boats did not make a decisive difference in the outcome of these battles. But, like the Kamikaze aircraft attacks, they levied a frightful cost on the men tasked to face them.
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Tom Laemlein
Tom Laemlein is a historian. While that might sound mind-numbingly awful to some, he enjoys it. His deep dives into historical research keep him (mostly) out of trouble and, yet, too often away from the rifle range. Tom is the author of more than 30 books on military history and weapons systems. He regularly contributes articles to national magazines and websites on military history and firearms topics, and historical photos from his collection are used by publishers around the world. In those times that he is cornered in a corporate environment, he will talk about marketing until he is released. Tom is married to a very patient woman, and they live on America’s North Coast, near Lake Ontario. His regular misadventures with Wally, his young Tibetan Mastiff, remind him that life must be enjoyed full-bore, at least until you are ready for a nap.
November 21st, 2023
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