How America’s Mark 18 Torpedo Made Japanese Convoys Completely N.a.k.e.d And Defenseless

September 3, 1943. The sea was a sheet of molten silver beneath the dawn light, calm and deceptive, its stillness broken only by the faint hum of machinery deep below the surface. Four hundred miles southwest of Truk Lagoon, Commander Eugene Sans stood inside the conning tower of the USS Spearfish, peering through his periscope as a Japanese convoy cut steadily across the horizon. Seven cargo ships and two escorts—fat, slow-moving targets spread neatly across the water like pieces on a chessboard. For Sans and his crew, it was the kind of opportunity submarine commanders dreamed about. Yet that morning, as the Spearfish prepared to strike, the captain’s pulse carried an edge of apprehension he could not quite shake.

They had orders from Pearl Harbor to test a new weapon—something revolutionary, something that promised to change the rules of submarine warfare in the Pacific. Packed inside Spearfish’s torpedo tubes were the Navy’s newest experimental weapons: the Mark 18 electric torpedo. They were sleek, strange things, matte gray and whisper-quiet, driven not by the shrieking combustion of steam but by electricity. They left no trail of bubbles, no shimmering wake to betray a submarine’s position. Theoretically, once fired, they were ghosts.

Sans had read the reports before leaving port. The Mark 18 was modeled on captured German technology, an electric torpedo the Germans had used to terrorize Allied shipping in the Atlantic. American naval intelligence believed that if the Mark 18 performed as advertised, it could turn the Pacific into a graveyard for Japanese shipping. Every convoy, every freighter, every destroyer escort that once relied on spotting the bright bubble trail of American torpedoes would be left blind. The Japanese, so confident in their sonar, their depth-charge patterns, and their surface radar, would suddenly find themselves fighting phantoms.

But as Sans steadied his scope, adjusting the focus on the lead freighter’s silhouette, he couldn’t ignore the tension humming through the control room. His crew had been whispering about the new weapons ever since they’d loaded them aboard. The mechanics didn’t trust the batteries. The fire-control team said the gyros were unreliable. Even his executive officer, a man who rarely voiced an opinion, had muttered, “They look like they were built by someone who’s never been to sea.”

Still, orders were orders. Sans had been a submariner long enough to understand that progress in wartime was always born of risk. The only way to learn what a weapon could do was to use it.

“Range to target?” Sans asked quietly.

“Four thousand yards, sir,” came the reply.

He nodded. “Set depth to eight feet. Stand by to fire.”

The Spearfish drifted silently through the dark waters, her engines throttled down, her hull creaking softly as she adjusted trim. Inside, the air was tense and stale, every man waiting for the moment the captain would give the order that could change the course of the war—or sink them all.

Sans took one last look through the scope. The lead ship’s flag rippled faintly in the morning light. Perfect conditions. No crosswind. No heavy swell. No reason the new torpedoes shouldn’t perform exactly as promised.

“Fire one,” he said.

The Mark 18 left its tube with a deep, muffled thump. It accelerated smoothly, its electric motor emitting only a faint mechanical hum. The men leaned forward, straining to hear something—anything—beyond the rhythmic ping of the sonar. Through the periscope, Sans caught a faint shimmer below the surface where the torpedo had gone, but there was no telltale trail, no frothy line of bubbles pointing back toward them.

For the first time, he felt it—the thrill of potential. The torpedo vanished into the water like a ghost. He turned his attention to the convoy, watching, waiting.

Then the shimmer veered abruptly to the right. The torpedo fishtailed, spiraled, and disappeared into the depths.

Sans lowered the scope, jaw tight. “Fire two.”

The next torpedo launched perfectly, clean and quiet. It tracked straight for several hundred yards, a phantom blade slicing toward the enemy formation. Then, without warning, it broached the surface—bursting up like a startled dolphin—before diving erratically and vanishing.

“Fire three,” Sans ordered, the words sharp.

The third torpedo struck the inner door on launch, a grinding metallic shriek echoing through the hull. The sound sent a chill through the compartment.

The fourth sank the moment it cleared the tube.

One by one, the Mark 18s failed in new and imaginative ways. Some ran too deep. Some circled wildly. One went rogue entirely, forcing the Spearfish to dive deep to avoid being hit by its own weapon. Others struck the target lines perfectly but detonated far too early or not at all. After fifteen launches, the results were disastrous.

Sans stood silent, hands braced on the edge of the periscope housing, his jaw locked as his XO read the failure reports aloud. Every torpedo had either malfunctioned or missed. His logbook would later record the results with understated fury: “Performance unsatisfactory. Accuracy inconsistent. Reliability doubtful.”

Up above, Japanese lookouts scanned the water, alert and puzzled. They had seen the flashes of movement—the shimmer of something beneath the surface—but no wake, no sign of approaching danger. They watched the American attack unfold like spectators, the freighters continuing on undisturbed. The absence of explosions was reassuring. The absence of bubble trails, however, was unsettling.

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September 3rd, 1943, 400 m southwest of Truck Lagoon, Commander Eugene Sans stood in the conning tower of USS Spearfish, watching through his periscope as a Japanese convoy steamed across the horizon. Seven cargo ships, two escorts, perfect targets for what should have been a revolutionary new weapon.

 Sans had received his orders just days before departure from Pearl Harbor. His submarine carried Mark 18 torpedoes, America’s first electric torpedo. A weapon that promised to solve one of the most fundamental problems in submarine warfare. The telltale wake of bubbles that pointed directly back to the firing submarine like a signpost reading, “Shoot here.” The Mark 18 left no wake. It ran silent.

 It was based on captured German technology that had terrorized Allied shipping in the Atlantic. American naval intelligence believed this weapon would revolutionize submarine warfare in the Pacific, transforming American boats from vulnerable hunters forced to dive immediately after firing into patient killers who could stalk convoys with impunity.

 What Sans was about to experience would reveal a truth that neither American engineers nor Japanese naval planners yet understood. The electric torpedo, even with its initial teething problems, represented a technological shift that would make Japanese anti-submarine warfare doctrine obsolete. Japanese escort commanders had learned to spot the wake of American Mark14 torpedoes, to count the seconds after launch to calculate the firing submarine’s position and attack it with depth charges.

 Those tactics, refined through two years of combat, were about to become worthless. The mathematics of submarine warfare were being rewritten, and the Japanese Navy, confident in its ability to counter the American submarine threat, had no idea that the rules of engagement were changing beneath them. SANS gave the order to fire.

 The first Mark1 18 left its tube with a distinctive thump, accelerating smoothly as its electric motor spun up to speed. No trail of bubbles followed it. No exhaust plume marked its path. Through his periscope, Sans watched the torpedoes track, a ghostly disturbance in the water visible only because he knew exactly where to look.

 Then the torpedo fishtailed violently, swerved off course, and disappeared into the depths. The second torpedo launched cleanly, ran straight for 300 yd, then broached the surface like a breaching whale before diving erratically and vanishing. The third torpedo hit the submarine’s outer door on launch, causing metallic screeching that echoed through Spearfish’s hull. The fourth sank immediately after leaving the tube.

 Over the next hour, Sans fired 15 more torpedoes. One ran wild, forcing Spearfish to dive deep to avoid being hit by her own weapon. Three more malfunctioned in various spectacular ways. Seven missed a stern by wide margins, their depth control systems sending them beneath targets, or their gyroscope mechanisms steering them in random directions. The results, as Sans would write in his patrol report with controlled fury, were disappointing.

Japanese lookouts on the convoy escorts watched the American attack with professional interest. They spotted no torpedo wakes. They observed the freigherss continue steaming placidly. If you’re enjoying this deep dive into the story, hit the subscribe button and let us know in the comments from where in the world you are watching from today. They concluded correctly that most of the American torpedoes had malfunctioned.

What they did not understand was the significance of what they were not seeing. The absence of those telltale bubble trails represented a technological capability that once perfected would render their entire anti-submarine doctrine obsolete.

 The Japanese Navy’s response to this first encounter with American electric torpedoes would prove to be one of the war’s most catastrophic intelligence failures. The story of the Mark 18 begins not in American shipyards or research laboratories, but on the beaches of occupied France in 1942. German hubot dominated the Atlantic, sinking Allied merchant ships faster than they could be replaced.

 The weapon responsible for much of this carnage was the G7E electric torpedo, a design fundamentally different from the steamdriven torpedoes that every other Navy relied upon. While American, British, and Japanese torpedoes used compressed air and fuel to drive turbines, leaving long trails of bubbles, the German G7E ran on battery power.

 It was slower than conventional torpedoes, achieving only 30 knots compared to the 45 knots of the American Mark14. Its range was shorter, just 4,100 yd compared to the Mark1 14’s 9100 yd at slow speed. But the G7E possessed two enormous advantages. First, it left virtually no wake. The electric motor produced no exhaust, no stream of bubbles, nothing to alert targets or reveal the firing submarine’s position.

 Second, it was far simpler to manufacture. German factories produced G7E torpedoes, using about 66% of the labor required for conventional torpedoes. Fewer skilled workers meant faster production, a critical advantage for Germany’s strained wartime economy. The Royal Navy understood the threat these weapons posed.

 British anti-submarine forces hunting U-boat in the Atlantic had learned that German submarines could attack convoys, sink ships, and escape before escorts could pinpoint their location. The absence of torpedo wakes gave U-boat precious seconds, sometimes minutes, to clear the area before depth charges began falling. In early 1942, several German G7E torpedoes washed ashore on beaches in France and England after being fired at targets and missing.

 British intelligence recovered these weapons intact, examined them thoroughly, and shared their findings with American naval intelligence. The torpedoes revealed a sophisticated design that German engineers had perfected through years of development. Lead acid batteries powered a direct current motor rated at 90 horsepower.

 Pneumatic controls regulated depth and steering. Proven technology that avoided the complexity of electric control systems. The warhead contained 575 lb of explosive. Less than the Mark1 14’s 643 lb, but still more than adequate to sink a merchant ship or a warship. Admiral Ernest King, Chief of Naval Operations, reviewed the intelligence reports with keen interest.

 The United States Navy had been working on its own electric torpedo designs since the 1920s, but progress had been glacially slow. The Naval Torpedo Station at Newport, Rhode Island, responsible for torpedo development, had spent over 20 years producing a designated Mark 20 that remained perpetually in development, never quite ready for combat use. King was facing a torpedo crisis of his own.

 The Mark 14, America’s standard submarine torpedo, had proven catastrophically defective. Submarine commanders reported that torpedoes ran too deep, exploded prematurely, or failed to detonate even when they struck targets directly. By mid 1942, Admiral Charles Lockwood, commanding submarines in the Southwest Pacific, had documented these failures so thoroughly that even the Bureau of Ordinance, which had spent two years denying any problems existed, could no longer maintain its position.

 The Mark1 14’s defects were being fixed slowly and against bureaucratic resistance that bordered on sabotage. But even a perfected Mark14 would still leave awake. Every time an American submarine fired, it announced its presence to every escort vessel in the area. King saw an opportunity. The captured German torpedoes provided a proven design that could be copied quickly.

 The Mark 20, despite two decades of development, was nowhere near combat ready. Rather than wait for Newport to perfect its own design, King ordered the Bureau of Ordinance to copy the German weapon, build it exactly as the Germans built it, put it into production immediately. The submarine force needed electric torpedoes, and it needed them now. The Bureau of Ordinance reacted with barely concealed hostility.

 Newport had been developing electric torpedoes for 20 years. The Mark 20 represented the culmination of that effort, incorporating cutting-edge features and American engineering principles that the bureau insisted were superior to German designs. Ordering them to copy a German weapon implied that their own work was inadequate. The bureau was delayed.

 It demanded time to study the German torpedoes more thoroughly. It proposed modifications to improve the German design. additions that would require months of testing. It suggested that perhaps the Mark 20 could be accelerated instead. King was not interested in bureaucratic territoriality. He sent direct orders. Copy the German torpedo.

Do it now. Do not modify it. Do not improve it. Build it exactly as captured. If Newport cannot or will not do this, the contract will go to a private company that will. The message was clear enough that even the Bureau of Ordinance understood. Work began in May 1942.

 The Westinghouse Electric Corporation received the primary contract to manufacture what would be designated the Mark 18 torpedo. Westinghouse had no experience building torpedoes, but it had extensive experience with electric motors and battery systems. The Exide Battery Company would provide the lead acid batteries that powered the weapon. Both companies faced enormous challenges. The German G7E had been designed for production in German factories using German tools, German materials and German manufacturing tolerances.

 American factories used different standards converted from metric to imperial units. Materials had to be sourced from American suppliers producing to American specifications. Most critically, the torpedo required extraordinarily fine tolerances, precision work that demanded skilled machinists. But 1942, America was mobilizing for total war.

 Skilled workers were being drafted into the military as fast as they could be trained. The labor force available for torpedo production consisted largely of workers with minimal experience. The batteries posed their own problems. The Exide batteries did not deliver the hoped for performance.

 They generated excessive amounts of hydrogen gas during operation. A fire hazard on any ship and potentially lethal on a submarine where one spark could trigger an explosion that would kill everyone aboard. The battery chemistry needed adjustment, but any change required extensive testing to verify that performance remained acceptable. Testing took time.

 Time measured in months. While submarine commanders in the Pacific fought with inadequate weapons, production bugs multiplied. The fine tolerances required for the torpedoes propulsion system meant that minor variations in manufacturing could cause catastrophic failures.

 Quality control became a nightmare as inexperienced workers struggled to meet specifications they barely understood. By July 1943, over a year after the program began, production was finally ramping up. But the torpedoes reaching Pearl Harbor were far from perfect. Commander Oliver Kirk, commanding USS Lapon, was ordered to Newport to assist with testing. Kirk was an experienced submarine officer who understood torpedoes intimately.

 What he found at Newport shocked him. The Naval Torpedo Station staff treated the Mark1 18 program with barely concealed contempt. These were not American-designed torpedoes. They were copies of enemy weapons built by companies that had never manufactured torpedoes before. Newport’s torpedo experts had spent their careers perfecting American designs.

 Being ordered to support a German copy insulted their professional pride. Kirk’s executive officer, Eli Reich, would later describe Newport’s attitude as near to sabotage. The torpedo station refused to share test data with Westinghouse. They declined to provide technical assistance when production problems arose. They offered no suggestions for improving manufacturing processes.

 Most damningly, they withheld information about operational problems discovered during testing, forcing submarine commanders to discover these defects themselves in combat. Kirk and Reich drafted a scathing memorandum documenting Newport’s obstruction. That memo reached Admiral Lockwood’s desk.

 Lockwood, who had spent two years fighting the Bureau of Ordinance over the Mark 14’s defects, recognized bureaucratic sabotage when he saw it. He took the matter directly to Rear Admiral William Spike Blandi, chief of the Bureau of Ordinance. Bland had spent months defending the Mark1 14 while dismissing submarine commander complaints as operator error. He had resisted every effort to test the MarkV properly, insisted that the torpedoes worked perfectly, and blamed failures on poor maintenance and incompetent shooting. Only overwhelming evidence had finally forced him to admit the Mark 14

was defective. Now Lockwood was telling him that Newport was deliberately obstructing the Mark1 18 program. Blandi, to his credit, understood that further obstruction would cost American lives. He ordered Newport to cooperate fully with the Mark 18 program. He assigned additional personnel to support production.

 He made clear that anyone continuing to obstruct the program would face consequences. Progress accelerated, but slowly. The first Mark1 18 reached the submarine base at Pearl Harbor in May 1943. They were still not perfected. Hydrogen generation remained a problem. Depth control was erratic. Some torpedoes ran too deep, others too shallow.

 Gyroscope failures caused torpedoes to run wild or circle back toward their own submarines. The contact exploders, copied directly from German designs, proved no more reliable than the Mark1 14’s exploders had been before their redesign. Commander Dudley Mush Morton, perhaps the most famous submarine commander in the Pacific Fleet, took USS Wahoo on patrol in September 1943 with Mark 18 torpedoes aboard.

 Morton was a legend credited with sinking over 60,000 tons of Japanese shipping. Famous for his aggressive tactics and his willingness to take risks that more cautious commanders avoided. If anyone could make the new electric torpedoes work, Morton could. Wahoo entered the Sea of Japan through La Peru Strait, threading between Sakalin Island and northern Japan, penetrating into waters that the Japanese considered safe from submarine attack.

 Morton found rich hunting grounds, convoys steaming without heavy escort, merchant ships sailing independently because Japanese commanders believed no American submarine could reach these waters. Morton attacked. The Mark1 18 torpedoes performed erratically. Some ran true, striking targets and detonating properly. Others malfunctioned in the ways that had become grimly familiar to American submarine commanders, running too deep, exploding prematurely, refusing to detonate on impact. But enough torpedoes worked.

 Morton sank four ships totaling 15,000 tons before Japanese anti-submarine forces located Wahoo and began hunting her. On October 11th, 1943, Japanese aircraft spotted Wahoo transiting La Peru Straight on the surface, attempting to clear Japanese waters before daylight forced her to submerge. The aircraft attacked immediately, dropping depth charges that struck near the conning tower.

 One charge detonated close enough to jam Wahoo’s diving controls. The submarine, unable to dive, died on the surface, and a repeated bombing attacks. 80 men went down with her, including Morton himself. News of Morton’s death stunned the submarine force.

 He had been invincible, the one commander who seemed immune to the dangers that claimed other boats. His loss demonstrated that even the best commander with the best crew could die because equipment failed at the wrong moment. The submarine community mourned Morton. But they also noted something significant. Wahoo had successfully used Mark1 18 torpedoes in combat.

Despite their problems, despite their erratic performance, the electric torpedoes had sunk ships. And critically, Japanese anti-submarine forces had not used torpedo wakes to locate Wahoo. The submarine died because aircraft spotted her on the surface, not because escorts tracked her torpedo wakes to her firing position. That distinction mattered.

 Commander Eugene Sans’s disastrous first patrol with Mark 18 on Spearfish became a case study in everything that could go wrong. Of the torpedoes he fired, 30% malfunctioned completely. The submarine community reviewed his patrol report with grim attention to detail. Every failure was documented, categorized, analyzed.

 Engineers at Pearl Harbor and Newport examined torpedoes returned from patrol, dissecting failure modes, searching for patterns. The problems broke down into several categories. First, the torpedoes were too fragile for the launching forces involved. The Mark 18’s electric motor produced full power almost instantly, unlike the Mark 14 steam turbine, which took time to spin up to speed.

 This instant acceleration subjected the torpedo to enormous stress as it left the tube. The torpedo’s thin skin could not handle the shock, causing structural failures that ranged from minor leaks to catastrophic implosion. Second, the depth control system, copied directly from the German design, had been calibrated for German operating conditions.

In the Pacific, water temperatures and salinity differed from the Atlantic and Baltic, where Germans had tested their torpedoes. These differences affected the hydrostatic depth sensor in ways German engineers had never encountered.

 Torpedoes set to run at 10 ft depth might actually run at 25 ft or at 5 ft depending on water conditions. Third, the gyroscope steering mechanism proved vulnerable to the shock of launch. Gyroscopes are delicate instruments containing rapidly spinning rotors. Launch forces could knock these rotors off balance, causing the torpedo to veer wildly off course or circle back toward the firing submarine.

 This last defect was potentially lethal. The submarine Tang would be sunk by one of her own torpedoes in October 1944, possibly a Mark 18 that circled back and struck her. Fourth, the batteries continued generating dangerous amounts of hydrogen gas.

 Submarine crews developed elaborate procedures for burning off the hydrogen safely. Everyday, heating coils in the battery compartments would be ignited, compressed air blown in to support combustion, and the hydrogen burned away in a controlled manner. The procedure worked mostly, but on at least one occasion, the heat generated was sufficient to melt the torpex warhead, causing explosive material to run out of the weapon like molten wax. Submarine commanders faced a choice.

 They could use the familiar Mark14s, now finally fixed after 2 years of modifications, which worked reliably, but left telltale wakes. Or they could use the Mark18, which left no wake but malfunctioned frequently and required constant maintenance. Initially, most commanders chose Mark1 14s, better a weapon that worked and left awake than one that failed at critical moments.

But a few commanders intrigued by the tactical advantages of weightless torpedoes persisted with Mark 18. They learned through painful experience how to employ them effectively. Fire from longer ranges to give unstable torpedoes time to settle onto their proper course. Fire more torpedoes per target to compensate for the higher failure rate.

Avoid firing at steep angles where gyroscope errors would be magnified. Accept the need for constant maintenance. checking battery levels, testing circuits, examining seals. By late 1943, Mark 18 were achieving modest success rates. Not spectacular, not comparable to the now reliable Mark1 14s, but good enough to prove their tactical value.

 Japanese convoy escorts, accustomed to spotting torpedo wakes and calculating firing positions, found themselves unable to locate submarines that fired electric torpedoes. The escorts would patrol the area where a submarine should have been, drop depth charges on suspected locations, and achieve nothing.

 The submarines escaped unscathed to attack again hours later or the next day. Japanese naval intelligence compiled reports on these attacks with growing unease. American submarines were achieving higher success rates. Convoys were losing ships despite escort vessels performing their duties properly.

 Most troubling, escorts were failing to sink attacking submarines even when they reached the attack area quickly. The statistics documented the problem. In early 1943, before Mark 18 entered service in significant numbers, Japanese escorts sank or severely damaged approximately 8% of American submarines that attacked convoys. By late 1943, that figure had dropped to less than 4%.

 The change correlated directly with increasing Mark18 use. Japanese anti-submarine doctrine had been built on the assumption that torpedo wakes revealed submarine positions. Escort commanders had developed standard responses refined through hundreds of engagements. Spot the wake. Calculate the torpedo’s course. Extrapolate backwards to determine firing position. Steam at maximum speed toward that position.

 begin dropping depth charges in a pattern centered on the calculated location. Continue the attack until the submarine was destroyed or driven so deep it could not continue combat operations. This doctrine worked brilliantly against Mark1 14 torpedoes with their conspicuous bubble trails. It failed completely against Mark 18.

 Escort commanders observing cargo ships torpedoed without warning, without visible torpedo tracks, struggled to understand what was happening. Some concluded that American submarines had perfected a new type of long range torpedo that could be fired from beyond visual range. Others theorized that submarines were using multiple submarines in coordinated attacks, firing from several directions simultaneously. A few correctly deduced that American torpedoes were now leaving minimal or no wakes, but this conclusion

was rejected by higher headquarters as implausible. The Grand Escort Command headquarters established in November 1943 to coordinate convoy protection, analyzed these reports, and reached incorrect conclusions. American submarines, the headquarters assessed, were employing new tactics, possibly multiple boats attacking simultaneously.

 The solution was to increase the number of escorts per convoy and improve coordination between escorts. What the headquarters failed to understand was that more escorts using the same doctrine would achieve nothing if they could not locate attacking submarines. The problem was not insufficient escorts. The problem was that the fundamental premise of Japanese anti-submarine warfare using torpedo wakes to locate submarines no longer worked.

 By early 1944, Westinghouse and Exide had resolved most of the Mark18’s teething problems. A redesigned battery reduced hydrogen generation to manageable levels. Modified launch guides in submarine torpedo tubes reduced the stress of launch, preventing structural failures. Improved gyroscope mounting systems reduced the frequency of wild runs and circular runs. Most importantly, production had accelerated to the point where submarines could load full complements of Mark 18 if commanders wished.

 The torpedo remained slower than the Mark1 14, just 29 knots compared to 45 knots. Its range remained shorter, 4,000 yd compared to 9,000 yd. But increasingly, submarine commanders decided these limitations were acceptable prices to pay for the tactical advantage of leaving no wake. The shift in preferences showed up clearly in usage statistics.

 In 1943, Mark 18 accounted for less than 15% of torpedoes fired by American submarines. In 1944, that figure rose to 30%. By 1945, Mark 18 represented 70% of torpedoes expended with Mark1 14s relegated to situations requiring high speed or long range.

 This shift occurred because submarine commanders understood something Japanese escort commanders did not. Modern submarine warfare was as much about survival as about sinking ships. A submarine that sank two freighers but was then located and sunk by escorts had failed strategically. A submarine that sank one freighter but escaped to patrol another day was far more valuable.

 The Mark1 18, despite its limitations, dramatically improved submarine survivability. Japanese convoy escort doctrine had evolved to counter the Mark1 14. It could not adapt quickly enough to counter the Mark1 18 because doing so would require abandoning tactics that had been proven effective over two years of combat.

 The case of convoy HI72 in September 1944 illustrates how completely Japanese anti-submarine warfare had failed to adapt. The convoy consisted of 14 merchant ships carrying reinforcements from Singapore and Manila to the home islands.

 The escorts included three destroyers and two smaller patrol vessels, a substantial force by Japanese standards at this stage of the war. American codereers at Pearl Harbor had decrypted Japanese naval messages detailing the convoys route, speed, and schedule. Three American submarines, USS Growler, USS Salon, and USS Pampanito were positioned to intercept. On September 12th, 1944, Growler made contact with the convoy in the South China Sea.

 Commander Thomas Oakley maneuvered his boat into attack position at periscope depth. The convoy was zigzagging, standard Japanese practice, with escorts positioned on the flanks and ahead of the merchant ships. Oakley fired six Mark 18 torpedoes at two large transports. The torpedoes left their tubes silently, accelerated smoothly, left no visible wakes in the calm tropical water.

 Japanese lookouts on the escorts scanning the horizon with binoculars saw nothing. No bubble trails pointing toward a submarine. No disturbance in the water. The first indication of attack came when torpedoes struck home. The transport Aiden Maru took two hits amid ships. The explosions broke her back and she began sinking immediately.

 The transport Taiima Maru took one hit that flooded her engine room and stopped her dead in the water. The convoy’s senior escort commander aboard the destroyer Asaka Maru reacted immediately. He ordered all escorts to begin anti-submarine search patterns, radioed for air support, and commanded the remaining merchant ships to scatter.

But where should the escorts search? In previous attacks, escorts had used torpedo wakes to calculate submarine positions. Now there were no wakes, no evidence of where the attacking submarine had been when it fired. The escorts began dropping depth charges in a wide pattern around the stricken transports, hoping to catch the submarine somewhere in the general area. But the general area covered several square miles of ocean.

 Growler, having fired and heard the explosions through her hull, simply motored away at 5 knots, remaining at periscope depth, watching the chaos unfold behind her. The escorts never came close. Hours later, after sunset, Growler surfaced to recharge her batteries. Oakley radioed Selon and Pampanito with updated convoy information.

 The three submarines coordinated their attacks for the following day. On September 13th, all three boats attacked the scattered convoy. They sank five more ships. The escorts, despite aggressive depth charging and extensive patrols, damaged none of the submarines. When convoy HI72 finally limped into port, it had lost seven of 14 merchant ships, over 50% casualties.

 The escorts filed detailed action reports, noting that they had been unable to locate attacking submarines because torpedo wakes were either not visible or completely absent. These reports reached Grand Escort Command headquarters where staff officers analyzed them with increasing concern. The conclusion was inescapable. American submarines had perfected weightless torpedoes.

 But this conclusion, while correct, came too late to implement effective countermeasures. Countering weightless torpedoes required fundamental changes to Japanese anti-submarine doctrine. Escorts needed to patrol larger areas around convoys because submarines could now attack from positions previously considered too distant. That required more escort vessels.

 But Japan’s ship building industry could barely replace combat losses, let alone expand the escort fleet. Escorts needed better sonar to detect submarines before they reached firing positions. But Japanese sonar technology lagged years behind American and British equipment, and closing that gap required research and development time Japan no longer had.

 Most critically, escorts needed aggressive commanders willing to actively hunt submarines rather than simply react to attacks. But aggressive hunting required steaming at high speed, which made sonar useless due to the noise generated by the escort’s own propellers. The Japanese Navy found itself trapped by a doctrinal contradiction.

 Their escorts could not locate submarines after attacks because there were no torpedo wakes to indicate firing positions. They could not prevent attacks because their sonar was inadequate to detect submarines before they reached firing range. And they could not hunt submarines aggressively because doing so blinded their own detection equipment.

 If you find this story engaging, please take a moment to subscribe and enable notifications. It helps us continue producing in-depth content like this. The mathematics were brutal and simple. American submarines using Mark1 18 torpedoes achieved higher success rates with lower losses than submarines using Mark1 14s. The difference was not enormous.

 perhaps 20% improvement in ships sunk per patrol with a 50% reduction in submarines lost or damaged by escorts. But over hundreds of patrols, those percentages accumulated into devastating aggregate effects. The Pacific War entered 1945 with Japan’s merchant marine on the verge of complete collapse.

 American submarines had been sinking Japanese shipping at rates far exceeding replacement capacity since mid 1943. The introduction of Mark1 18 torpedoes in significant numbers from late 1943 onward accelerated this destruction. In January 1945, American submarines sank 252,000 tons of Japanese merchant shipping. In February, 182,000 tons. In March, 269,000 tons.

 Japan’s shipyards, even operating at maximum capacity, could build perhaps 300,000 tons per year total, assuming they had steel, electricity, and workers, all of which were increasingly scarce. American submarines were sinking the equivalent of Japan’s entire annual ship building capacity every month. Individual submarine patrols during this period achieved results that would have seemed impossible in 1942.

 USS Barb, commanded by Commander Eugene Flucky, sank 17 ships totaling over 96,000 tons on a single patrol, setting a record that would never be exceeded. Barb was equipped with Mark 18 torpedoes for the majority of her attacks. Flucky had learned to exploit their tactical advantages, approaching convoys from unexpected directions, firing from ranges where escorts did not expect threats, using the lack of torpedo wakes to remain undetected even after multiple attacks.

 On one memorable occasion in June 1945, Flucky took Barb into Namuan Harbor on the China coast, threading through shallow water that Japanese commanders considered impossible to submarines. The harbor was filled with merchant ships that had sought shelter from American submarines prowling offshore. Flucky fired every torpedo aboard, 24 Mark18, in a devastating attack that sank four ships totaling over 15,000 tons in less than an hour. Japanese shore batteries fired at suspected submarine positions.

 Patrol boats dropped depth charges in frantic patterns. They never located Barb, which escaped through the same shallow channel she had entered, surfacing miles offshore to radio her success. The Japanese garrison commander at Namuan filed a report stating that his defenses had been rendered useless by American weapons that left no trace of their passage.

 He recommended abandoning the port as a refuge for merchant shipping because submarines could attack with impunity. The Grand Escort Command headquarters forwarded this report to Imperial Naval General Headquarters with a grim assessment. American submarines now dominated Japanese coastal waters. Convoys sailing between Japan and occupied territories faced losses approaching total annihilation.

 Merchant ships attempting to reach Japanese ports were being sunk at such rates that insurance companies refused to underwrite voyages. captains and crews, civilian merchant sailors who had military obligation to sail into certain death, were deserting their ships in port rather than face American submarines. The assessment concluded with a stark recommendation. Japan should suspend most maritime traffic and husband its remaining merchant vessels for absolutely critical supply runs only.

 This meant abandoning outlying garrisons to starvation, halting imports of raw materials from Southeast Asia, accepting that Japan’s war economy would grind to a complete halt. Imperial Naval General Headquarters did not formally accept this recommendation. Doing so would have been tantamount to admitting defeat, but in practice, Japanese maritime operations collapsed to minimal levels by summer 1945.

 The few ships that still dared to sail did so, hugging the coast, staying in shallow water where submarines could not follow, moving only at night with no lights showing, hoping to escape notice. This defensive posture represented complete strategic defeat. Japan was an island nation that required seaborn trade to survive.

 Cutting that trade meant cutting off oil from the Dutch East Indies, rubber from Malaya, rice from Indochina, iron ore from China. Without these imports, Japanese industry could not operate. Without industry operating, the military could not sustain combat operations. The entire apparatus of modern warfare ground to a halt. The Mark 18 torpedo accounted for approximately 1 million tons of the 4.

8 8 million tons of Japanese merchant shipping sunk by American submarines during the Pacific War. This represented roughly 21% of total submarine kills achieved with approximately 30% of torpedoes fired. The statistics indicated that Mark 18 were slightly less effective per torpedo fired than the improved Mark1 14s, probably due to their lower speed and shorter range. But focusing solely on tonnage sunk misses the Mark18’s true strategic value.

The weapon transformed submarine operations from high-risk one-shot affairs into extended campaigns where submarines could stalk convoys for days, attack repeatedly, and escape unscathed. This transformation changed the mathematics of the submarine war in ways that pure tonnage statistics do not capture.

 Before Mark 18 became common, a submarine might attack a convoy once, sink one or two ships, then be forced to withdraw because escorts would locate and depth charge the firing position. With Mark 18, submarines attacked repeatedly. Commanders like Eugene Flucky on Barb or Richard O’Ce on Tang would shadow convoys for days, attacking at dawn, diving deep while escorts searched fruitlessly, surfacing at night to pursue, attacking again at the next opportunity.

Japanese convoy commanders found themselves in a psychological nightmare. Ships were being sunk by invisible attackers who could not be located or deterred. Escorts dropped thousands of depth charges without scoring hits. Patrols searched thousands of square miles without finding submarines.

 The conviction grew among Japanese sailors that American submarines were invincible, that no convoy was safe, that sailing into the Pacific meant sailing to certain death. This psychological impact manifested in morale collapse across the Japanese merchant marine. Crews refused to sail. Officers resigned their commissions. Ships sat in port because no one would man them.

 Japan’s military government instituted increasingly draconian measures, threatening deserters with execution, conscripting civilian sailors into military service where they could be shot for refusing orders. These measures achieved little. Men forced to sail on ships they knew were doomed performed their duties with the minimum effort required to avoid punishment.

Lookout stared at empty horizons without really watching. Engineers maintained engines that would never complete another voyage. The entire system operated in a state of desparing futility. The irony of the Mark 18’s development and deployment was lost on neither American submarine commanders nor Japanese escort commanders.

 The weapon that devastated Japanese shipping was a direct copy of a German design that the United States Navy had initially dismissed as inferior to American engineering. The Bureau of Ordinance, which had spent decades developing its own electric torpedo designs, had been ordered to abandon that work and simply copy enemy technology.

 This represented a profound institutional humiliation for an organization that prided itself on technical superiority. Yet that copied enemy weapon, once American industry scaled up its production and American engineers fixed its teething problems, proved devastatingly effective. The Mark18 succeeded not because it was technologically superior to the Mark1 14, which by late 1943 worked reliably, but because it addressed a tactical requirement that the Mark1 14 could not meet.

 The absence of a visible wake changed the fundamental dynamics of submarine warfare in ways that no improvement to conventional torpedoes could match. Japanese escort commanders reading captured American documents and interrogating prisoners from sunken submarines learned that Mark 18 were based on German G7E torpedoes.

 This knowledge provided no useful intelligence for developing counter measures. Knowing the origin of a weapon does nothing to reduce its effectiveness. The Japanese Navy had encountered German electric torpedoes in the Mediterranean and Baltic, where Japanese submarines operated alongside German forces. In 1943 and 1944, Japanese naval observers filed detailed reports on German submarine tactics and weapons.

 These reports accurately described the G7E’s capabilities and the tactical advantages it provided. Japanese naval staff officers rid these reports and concluded that electric torpedoes offered marginal advantages insufficient to justify developing Japan’s own electric torpedo program. This assessment was technically correct in isolation.

 The G7E was slower and shorter ranged than conventional torpedoes. Its advantages in leaving no wake and requiring less manufacturing effort were real, but seemed insufficient to outweigh its disadvantages. What Japanese planners failed to anticipate was the cumulative effect of these marginal advantages across hundreds of submarine patrols.

 A 5% improvement in submarine survivability, multiplied across 200 patrols per year, meant 10 additional submarines returning safely that otherwise would have been lost. 10 submarines surviving meant 40 additional patrols the following year. 40 patrols meant perhaps 80,000 additional tons of shipping sunk.

 The mathematics of cumulative advantage compounding over months and years transformed marginal tactical improvements into strategic dominance. By the time Japanese naval planners understood this, Japan lacked the industrial capacity, the raw materials, and the time to develop its own electric torpedoes. Japanese factories were being bombed by American B29s operating from bases in the Maranas.

 Raw material imports had been cut to a trickle by the very submarines Japan now desperately needed to counter. Electrical generating capacity was insufficient to support existing military production, let alone new programs. The window for developing counter measures had closed. The decisive factor in the Mark18’s success was not technological sophistication, but industrial capacity.

 Westinghouse and Exide, companies with no previous torpedo manufacturing experience, ramped up production from zero to thousands of units per year in less than 18 months. This achievement reflected American industrial power operating at a scale Japan simply could not match. American factories produced over 33,000 Mark1 18 torpedoes between 1943 and 1945.

Production peaked at roughly 50 torpedoes per day in early 1945. Each torpedo required approximately 66% of the labor needed for a Mark14, meaning the same workforce could produce 50% more weapons. This labor efficiency mattered enormously in an economy where skilled workers were scarce and military demand for weapons of all types exceeded available production capacity.

 Japanese industry, by contrast, produced approximately 21,000 torpedoes of all types during the entire war. Japanese factories operated with chronic shortages of steel, copper, electrical components, and skilled labor. Production rates that had been adequate in peace time proved catastrophically insufficient for wartime consumption.

 Torpedoes were expended faster than they could be replaced, forcing Japanese submarines and surface combatants to ration weapons and decline attacks on targets that in earlier years would have been engaged without hesitation. The submarine USS Silversides provides a detailed case study in how Mark 18 torpedoes changed combat operations.

 Commander John Koy took silver sides on her 12th war patrol in January 1945 with a mixed load of Mark1 14 and Mark18 torpedoes. Koi was an experienced commander with five previous war patrols and a reputation for aggressive tactics tempered by careful planning. On January 18th, Silverides encountered a convoy of six merchant ships with three escorts in the Formosa Strait.

 Koi maneuvered into an attack position at dawn approaching from the west. so the rising sun would silhouette the convoy against the eastern horizon while his submarine remained in shadow. Standard doctrine called for firing a spread of torpedoes at multiple targets, then diving deep immediately to avoid depth charge attacks.

 Koi followed modified doctrine that had become standard for commanders using Mark 18. He fired four Mark 18 torpedoes at two large transports, waited to observe the results, then fired four more Mark 18 torpedoes at a third transport before finally diving. The first four torpedoes struck home after runs of approximately 3,200 yd. Both transports, later identified as the 7,000 ton engine Maru and the 6,000 ton Mikasa Maru, took fatal hits and began sinking.

 The second spread of four torpedoes also ran true, striking the 8,000 ton transport Tynan Maru and causing massive flooding. Japanese escorts reacted immediately, racing toward the stricken transports, searching for the torpedo wakes that should indicate submarine position. They found nothing. No bubble trails, no disturbance in the water beyond the wakes of the torpedoes themselves, which pointed toward the targets, not back toward the firing submarine. The escorts began dropping depth charges in a wide pattern centered on where they estimated

the submarine must have been when it fired. Their estimates were accurate. Silversides had been exactly where the escorts calculated, but Silversides was no longer there. After firing, Koi had simply motortoed away at periscope depth, moving at 5 knots, putting distance between his boat and the attack position. By the time depth charges began falling, Silverides was over a mile away, well outside the danger zone.

Koi remained at periscope depth, circling the area, watching the escorts exhaust themselves in futile attacks. When the escorts finally withdrew to shepherd the surviving merchant ships away from the area, Koi surfaced and pursued.

 That night, he attacked again, sinking one of the remaining transports with Mark 14 torpedoes fired from long range. The Mark1 14s left visible wakes, but Silversides was already diving by the time escorts could reach her position. The submarine escaped unscathed. Over 5 days, Koi shadowed the remnants of the convoy, attacking three more times, sinking a total of seven ships. Japanese escorts never damaged Silverides, never forced her to withdraw, never even came close to a successful depth charge attack.

 Koi’s patrol report credited the Mark1 18 torpedoes with enabling this success. The ability to attack without leaving visible wakes meant he could operate with impunity, attacking repeatedly without risk of retaliation. This pattern repeated itself across hundreds of submarine patrols in 1945. Commanders learned to exploit the tactical advantages Mark 18 provided, developing techniques that maximized the weapon strengths while minimizing its weaknesses.

 Fire from moderate ranges, 2500 to 3500 yd. Close enough for accuracy, but far enough that the torpedo’s slower speed was not disadvantageous. Use Mark 18 for initial attacks when surprise was critical and escorts were not yet alert. Save Mark 14 for long range shots or high-speed targets where the Mark 18’s limitations were prohibitive.

remain at periscope depth after firing to observe results and set up follow-on attacks. The cumulative effect of these tactics devastated Japanese maritime logistics. By July 1945, American submarines had achieved such complete dominance over Japanese sea lanes that they were running out of targets. Merchant ships large enough to be worth a torpedo were increasingly rare.

 Submarines found themselves attacking small coastal freighters, fishing boats, and sailing vessels that in earlier years would not have warranted attack. The fact that submarines were engaging such marginal targets indicated how thoroughly the Japanese merchant marine had been destroyed.

 Imperial Naval General Headquarters compiled statistics on merchant shipping losses that documented the catastrophe in precise numerical terms. In 1942, Japan began the year with 6 million tons of merchant shipping. Losses during 1942 totaled 1.1 million tons. New construction added 800,000 tons, leaving Japan with 5.7 million tons at year end, a manageable loss rate. In 1943, losses totaled 1.

8 million tons. New construction added 760,000 tons, leaving Japan with 4.6 6 million tons, still sustainable, barely. In 1944, losses totaled 3.9 million tons, over double the previous year. New construction added 1.7 million tons, a remarkable achievement given bombing damage to shipyards and shortages of materials, but still grossly inadequate.

Japan ended 1944 with 2.4 million tons of merchant shipping, less than half of 1942 levels. In the first seven months of 1945, losses totaled 1.5 million tons. New construction added less than 300,000 tons as shipyards were bombed and production collapsed. By August 1945, Japan possessed less than 1.2 million tons of merchant shipping, 20% of the capacity it had possessed in December 1941.

 These numbers translated into economic strangulation. Oil imports from the Dutch East Indies, which had averaged 4 million tons per year in 1942, dropped to 1.7 million tons in 1943, 600,000 tons in 1944, and virtually zero in 1945. Without oil, the Imperial Navy could not operate. Major warships sat in port because there was no fuel to sort.

 Training programs shut down because there was no fuel for training flights or training cruises. Industrial production collapsed because factories depended on oil for power generation and transportation. Food imports, critical for feeding Japan’s urban population, dropped from 4 million tons per year in 1942 to less than 1 million tons in 1945.

 Rice rations in Japanese cities were cut repeatedly as authorities struggled to distribute what little food reached port. By August 1945, urban Japanese were receiving approximately 1,300 calories per day below subsistence level. Starvation was not imminent but approaching. The Japanese government understood that continuing the war was economically impossible.

 Even if Japanese forces won every battle, even if American invasion forces were thrown back into the sea with catastrophic casualties, Japan could not sustain combat operations without maritime logistics. And maritime logistics had been destroyed by American submarines, firing torpedoes that Japanese escorts could not counter.

 The atomic bombs dropped on Hiroshima on August 6th and Nagasaki on August 9th, 1945 provided the Japanese government with a face-saving rationale to surrender. The official surrender announcement cited the atomic bombs as the reason Japan could no longer continue fighting. This was not entirely accurate.

 Japan had been strategically defeated months earlier when its merchant marine was destroyed and its economy strangled. The submarines, not the bombs, had delivered the decisive blow. But admitting that the war was lost because merchant ships could not sail was humiliating in a way that blaming defeat on revolutionary super weapons was not.

 The Imperial Japanese Navy, which had begun the war by attacking Pearl Harbor and had dominated the Pacific for 6 months, ended the war effectively immobilized in port. Unable to contest American control of the seas, unable to protect the maritime logistics that an island nation required for survival, the Mark18 torpedo, a weapon that American naval officers had initially dismissed as an inferior copy of enemy technology, accounted for a significant portion of the shipping losses that produced this outcome. The final irony of the Mark1 18 story emerges from postwar analysis and

the long-term trajectory of torpedo development. The United States Navy continued using Mark18 torpedoes after World War II ended. The weapons remained in the infantry through the 1950s, equipping submarines that patrolled during the early Cold War. Not until the 1960s when wire guided torpedoes and later acoustic homing torpedoes entered service did the Mark 18 finally become obsolete.

 The German G7E, which the Mark 18 team copied, remained in service with the West German Navy through the 1970s. Both weapons, despite being based on 1930s technology, proved so fundamentally sound that they remained combat effective for decades. The Newport Mark 20, the electric torpedo that the naval torpedo station had spent 20 years developing and that was supposedly superior to the German design, never entered service.

 After the war ended and production pressures eased, the Navy finally completed testing of the Mark 20. The tests revealed that the weapon offered no significant advantages over the Mark 18 and actually suffered from reliability problems that the Mark 18 had long since solved.

 The Mark 20 program was cancelled in 1946, a quiet admission that the Bureau of Ordinances decades of research had produced a weapon inferior to a design the Navy had copied from the enemy in 1942. This outcome vindicated Admiral King’s decision to copy German technology rather than wait for American engineers to perfect their own design. The submarine force needed electric torpedoes immediately.

 King had provided them immediately by bypassing institutional pride and accepting that sometimes copying success is wiser than pursuing perfection. For the Japanese Navy, the lessons of the Mark18 came too late to implement. Postwar interrogations of Japanese naval officers revealed that by mid 1944, Japanese submarine commanders understood that electric torpedoes offered substantial advantages.

 Several experimental Japanese electric torpedo designs were under development in 1944 and 1945. None entered production before the war ended. Japan simply lacked the time, resources, and industrial capacity to bring new weapons from conception to deployment. The Japanese submarine force, which had begun the war with excellent submarines and competent crews, spent most of the war employed in missions that wasted its capabilities.

 Japanese submarines were used primarily to supply isolated garrisons, transport material to beleaguered units, and evacuate personnel from islands about to fall. These missions, while necessary, did not exploit submarines primary capability, sinking enemy shipping. When Japanese submarines were finally released for commerce raiding in late 1944, they achieved modest success, but faced American anti-submarine warfare capabilities far superior to Japanese escort doctrine.

 American destroyers equipped with excellent sonar, radar, and depth charges, hunted Japanese submarines with ruthless efficiency. Of 83 Japanese submarines that conducted war patrols during the Pacific War, 56 were sunk, a loss rate of 67%, far higher than the American submarine forces 22%.

 The contrast between American and Japanese submarine warfare results from a complex of factors. Industrial capacity, intelligence from codereing, tactical doctrine, weapons reliability, and institutional culture. But the Mark18 torpedo represented a crucial element of American success. The weapon provided tactical advantages that American submarine commanders exploited brilliantly.

 Its development and deployment demonstrated American industry’s ability to scale up production of complex weapons rapidly. Its success validated Admiral King’s willingness to copy enemy technology when that technology worked. For submarine commanders like Eugene Flucky, Richard Oka, and thousands of officers and sailors served aboard American submarines, the Mark18 was the weapon that allowed them to prosecute the war without leaving calling cards for escorts to follow. It transformed submarine operations from desperate hit-and-run attacks into sustained campaigns that ground down Japanese maritime logistics month after month until nothing remained. Thank you for watching. For more detailed historical breakdowns, check out the other videos on your screen now.