In the early weeks of 1943, a Japanese torpedo came to rest on the sand at Point Cruz, Guadalcanal, without exploding. It was perfectly intact. American forces photographed it, disassembled it, packed it into crates, and shipped it home, where it was stood upright on the grass outside Navy headquarters in Washington. Every component was carefully measured.
Yet the one detail that had been sinking their ships escaped them entirely. The weapon on that beach was 30 feet long, two feet in diameter, and weighed roughly three tons. No weapon in American service came close to its specifications. The Mark 15 torpedo carried by U.
S. destroyers was 21 inches in diameter, weighed under two tons, and carried about 855 pounds of explosives. The warhead in the sand at Point Cruz held more than 1,000 pounds, and the filling was Shimose, seven percent more powerful than TNT by weight. Side armor on fleet cruisers and battleships was designed to absorb between 800 and 1,000 pounds.
This weapon was built to get through it. None of that was the secret. The secret was a steel flask running more than a third of the weapon’s total length, 11 and a half feet. Every marking on it indicated the word “air.
” Engineers at Kure deliberately labeled it that way. It contained pure compressed oxygen. Sailors handling the rounds at sea were told the flask was an auxiliary air vessel, so the men loading the tubes would not know what they were carrying. The Americans opened the flask, recorded the word “air,” and moved on.
The Bureau of Ordnance had been told plainly, and had decided in advance not to believe it. In 1940, the U. S. naval attaché in Tokyo, Commander Henry Smith-Hutton, contacted a source who had gone aboard a Japanese destroyer.
The man returned to say the ship’s torpedo tubes were larger than anything on record in Washington, and that a crew member had boasted their torpedoes ran on pure oxygen. Naval Intelligence forwarded the information, describing the source as unimpeachable. The Bureau of Ordnance assessed it and set it aside. Two reasons were given.
No Japanese design bureau could outdo its American counterpart, and the gas was too dangerous to put in a torpedo anyway. That second reason was not stupid. The Royal Navy had experimented with oxygen-enriched air in large torpedoes designed for its Nelson-class battleships in the 1920s and abandoned the idea. The Americans looked at it and stayed away as well.
Oxygen and kerosene explode on contact with the smallest trace of grease, and a torpedo is a machine full of grease. Japan solved that problem, and the solution was why the whole weapon worked. Every surface touched by the oxidizer was degreased and polished smooth, because any pit too small to see with the naked eye could retain a trace of oil, and that trace was enough to turn the cylinder into a bomb before the weapon left the launch tube. Engineers then added a third cylinder of about 13 liters, containing ordinary air.
The engine began running on air and fuel, its combustion steady. As that small cylinder lost pressure, oxygen seeped through a one-way valve and took over the burn. No one at Kure could make the engine ignite on pure gas, so they stopped trying. The payoff was simple arithmetic.
Air is about one-fifth oxygen and more than three-quarters nitrogen, so the same tank filled with pure gas held roughly five times the oxidizer. That translated into more distance, more speed, a heavier warhead, or a combination of all three. It also changed what came out of the weapon’s tail. The exhaust was carbon dioxide and water vapor, both of which dissolve in seawater.
Conventional torpedoes left a line of nitrogen bubbles on the surface pointing back to the ship that fired them. This one left virtually no trace. Side by side, the difference was stark. The Mark 15 could cover 15,000 yards at 26.
5 knots in its long-range setting, meant for throwing a dense volley at an enemy formation in hopes of a hit. The Japanese weapon could cover 22,000 yards at 48 to 50 knots, and more than 40,000 yards at 36 knots, while carrying half again as much explosive. The launch system was built around this torpedo, and this was the part the manuals consistently understated. Japan was alone among the world’s navies in equipping destroyers with reload torpedoes and rapid reload gear, doubling the firepower a single ship could put into the water in one battle.
Its cruisers carried heavy torpedo batteries as routine. Some destroyers mounted their launch tubes inside splinter-proof turrets. Just before the war, a few older light cruisers were converted into specialized torpedo ships, each carrying 40 torpedoes. Any ship carrying this weapon also needed an onboard oxygen generation plant to maintain it, no small thing to build into a destroyer.
Japan installed it anyway. It has often been said the U. S. Navy never thought about night torpedo operations.
That is untrue, and the war games prove otherwise. At the Naval War College, destroyer squadrons routinely executed heavy night fire. American planners recognized Japan needed a comparable weapon because the interwar treaties had left the Imperial Navy at a disadvantage in every tonnage ratio. U.
S. destroyers trained to deliver what they called “Browning attacks,” a whole squadron pouring everything along an enemy battle line on the theory that something had to hit. The phrase came from firing into a flock of birds without aiming at a particular one. The doctrine was sound.
The assumed range was wrong by a factor of two, and a factor of two meant everything. Commanders turned their course inside what they believed was torpedo range and settled outside it. Off Savo Island on the night of August 9, 1942, three American heavy cruisers and one Australian were sunk or destroyed in roughly half an hour, at least three of them hit by that large weapon. At Tassafaronga on November 30, eight enemy destroyers on a supply mission into Ironbottom Sound were surprised by a stronger force but fired anyway.
The destroyer Northampton sank. The cruisers Minneapolis, New Orleans, and Pensacola were badly damaged, and New Orleans lost its entire bow forward of the second turret. The explanations written afterward pointed to submarines. This was not a fabricated excuse to cover a disastrous night.
It was an honest conclusion by officers working from numbers they trusted. Casualties kept arriving from distances no surface ship could reach, so no surface ship had fired them, but something underwater had. On the rare occasions a stray round at full range hit a ship that was not its target, the conclusion was mines. In mid-1943, the Navy went after a wreck.
The destroyer Kikuzuki had taken a torpedo from a plane off the carrier Yorktown at Tulagi on May 4, 1942. She was beached at Gavutu by a submarine chaser but slid off with the next high tide and sank in Halavo Bay. She carried two triple 24-inch mounts and 10 rounds for them. American salvage teams raised her that summer.
Photographs taken in August show her out of the water alongside a crane barge. She was refloated by October 14 and towed to Purvis Bay, where she settled in shallow water and lies today. That wreck gave the U. S.
Navy its first conclusive proof that enemy destroyers carried 24-inch torpedoes. The oxidizer remained unidentified. The ordnance numbers remained far below the truth. Two teams, same theater, same year, with the hardware in their hands, and neither came back with the answer.
A cylinder that size is not a detail anyone can overlook. It is a detail that gets explained away and passed over. There was a third chance that year, on paper. Allied intelligence captured a Japanese book reviewing torpedo lessons from the early phase of the war and translated it.
The passages about the Type 93 drew no attention. Some of that traces to enemy discipline, and that discipline was real. Torpedo officers were forbidden to discuss these weapons with officers who had no connection to them. Speed, range settings, and the oxygen itself were kept out of the manuals used in torpedo schools.
Ships firing practice rounds recovered every single one afterward. The Imperial Navy also put out its own number, a claimed maximum of about 12,000 yards at 42 knots, less than a third of what the weapon could actually do. The same blindness covered something else already in American hands. Japanese night-vision optics were better than any other.
In night operations, they sometimes did more than early radar. U. S. officers captured and used them, but they were never entered into reference manuals at all.
Real understanding came in the spring of 1944, from prisoners and captured documents rather than the hardware itself. A February study on enemy naval weapons credited the weapon with 22,400 yards at 50 knots, close to correct. A March report based on interrogations and captured documents estimated between 32,700 and 30,800 yards at 32 knots, closer still. That same March report traced the design to a British oxygen-enriched torpedo Japan had obtained in 1924 or 1925.
Even then, American papers kept saying “enriched air” rather than oxygen, because “enriched air” was the term they knew, and their source material had been written by men told the cylinder contained air. The correction had to travel through the enemy’s own cover story before it reached Washington. Then, in July 1944, Naval Intelligence issued a new edition of its statistical summary of the Japanese Navy. It described the Type 93 as possibly the most radical and astonishing development in naval weapons to appear in the Pacific theater.
It estimated the warhead at 1,200 pounds, high but in the right range. It listed range at 11,000 yards at over 45 knots. Eleven thousand yards, four months after two separate reports estimated three times that, settling near the number Japan had published as a cover story. That office had another matter in 1943.
The Bureau of Ordnance spent two years insisting American submarine torpedoes worked fine while skippers returned saying the Mark 14 ran too deep, exploded early, or hit the target with no effect. That dispute was settled the same summer. The wreckage from Halavo Bay surfaced when Nimitz ordered magnetic exploders deactivated on June 24. An office that could not hear its own commanders was never going to hear a 1940 informant.
By the time the correct enemy numbers were circulating, the Imperial Navy no longer had the destroyers, the trained torpedo crews, or the sea room to fight as it had off Guadalcanal. The intelligence arrived after the problem had resolved itself. What lies in between can be counted. Twenty-two Allied warships were sunk after hits from the big torpedo: eight cruisers, ten destroyers, and the carrier Hornet.
Thirteen of them were destroyed by this weapon alone, with no bombs or gunfire involved. Houston went down in Sunda Strait, Quincy and Vincennes at Savo, and Juneau was crippled by a destroyer torpedo before a submarine finished her off. On the night of July 5–6, 1943, in Kula Gulf, the destroyer Strong was hit by a shot that traveled nearly 22,000 yards, one of the two longest torpedo hits of the entire war. The cruiser Helena sank in the same action from a distance that convinced the Americans a submarine had done it.
A 1943 model took a different direction, trading distance for destructive power: about 16,300 yards at 48 knots with the warhead increased to 1,720 pounds. Against protection designed to absorb half that force, the math was not complicated. That design fed everything that followed. A 21-inch version entered submarines as the Type 95.
A 17. 5-inch version went into midget submarines and was of little use. At the end of the war, the same engineering was scaled up into the Kaiten, a manned torpedo 15 meters long and eight tons, with a gyroscope spinning at 20,000 revolutions per minute and a warhead weighing more than a ton and a half. It was a double-edged weapon, and the Imperial Navy paid the price.
Shimose was shock-sensitive, and a warship carrying a full set of these rounds on deck under air attack carried its own destruction on the surface. Suzaya was lost off Samar when a near miss detonated the torpedoes in her starboard tubes and fire reached her magazines. Commanders under bombing had to decide whether to dump the things overboard first. On March 1, 1942, the heavy cruiser Mogami fired a spread of torpedoes that missed every target, then ran on to sink a Japanese minesweeper, two Japanese transports, a supply ship, and a hospital ship.
The destroyer Fubuki was blamed for years. The name everyone uses now was not used by anyone at the time. Samuel Eliot Morison, who wrote the Navy’s official history after the war, called it the Long Lance. The men targeted by it had no name for it because they did not know it existed.
As for the torpedo found at Point Cruz, the Navy never determined which ship had thrown it onto the sand. The caption on its photograph, filed under Guadalcanal campaign records as “unexploded torpedo,” says the weapon was fired by a submarine. It was not. No submarine anywhere carried a tube for a 24-inch round that long, which is precisely why Japan built a separate 21-inch version for its submarines.
This torpedo came from a destroyer or cruiser on a night no one recorded, aimed at a ship that never knew it was there. It stayed on the grass outside Navy headquarters in Washington for the rest of the war, nose pointed up so passersby could see its size. No one ever went back to correct that caption. No one went back to the 1940 records either; the informant Smith-Hutton relied on carries no name in any surviving American document.
One of these weapons still stands in the Navy yard today. Another is at Annapolis, in a small garden in front of Dahlgren Hall beside a walkway, with a Japanese aerial torpedo across the road next to it. The tank running a third of its length is empty now, and it still bears the marking that says “air.
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