When people think of naval warfare in the Pacific during World War II, they picture submarine captains locking onto targets, launching their torpedoes, and sending enemy ships to the bottom in a column of smoke and steel. That image, as dramatic as it may be, wasn’t always the truth. At least not early in the war. For nearly two years, American submariners went into battle with a torpedo that refused to do its job. It wasn’t the enemy that nearly broke their spirits. It was the Mark 14.
On July 24, 1943, the submarine USS Tinosa SS-283 faced a golden opportunity and watched it slip away as torpedo after torpedo failed to explode.
Lieutenant Commander Dan Daspit had his prey in sight. The massive 19,250-ton Japanese tanker Tonan Maru No. 3 was lumbering along, unescorted, a dream target. Daspit set up his approach by the book. Four Mark 14 torpedoes launched, textbook perfect. But instead of explosions, the crew of Tinosa heard the soul-sickening thump of metal on metal. All four torpedoes hit the target and did nothing.
Photo courtesy of combinedfleet.com
Frustrated but undeterred, Daspit stalked the target through the night and tried again. Two of his torpedoes finally worked. They slammed into the hull and knocked out the engine room. The ship stopped. It was wounded but not sinking. Daspit decided to pick her apart carefully. He closed in, set up perfect angles, and began firing one torpedo at a time. Over the course of the next hour, nine more torpedoes hit the target. None of them exploded.
One torpedo curved away before impact. Another struck the tanker and actually turned back in the water, as if confused. The scene felt less like a war patrol and more like a cruel prank. Daspit ordered the last torpedo held in reserve. He had it brought home. It would be evidence.
That single act, bringing back a live unexploded torpedo, finally shattered the silence surrounding one of the most shameful equipment failures in American military history. The Mark 14 had failed not because it was rushed into production, but because it was built under a philosophy that valued theory over proof. Testing had been minimal. No live fire trials had ever taken place against a ship’s hull. Torpedoes were expensive and the Navy didn’t want to waste them on target practice. Bureaucrats in the Bureau of Ordnance, BuOrd, thought their lab tests were enough. That assumption turned out to be costly.
The Mark 14 had a laundry list of flaws. It consistently ran too deep. It was supposed to explode beneath enemy hulls, where ships were most vulnerable. Instead, it passed under them and kept going. The magnetic exploder inside was supposed to detect the ship’s field and trigger the blast. That didn’t happen. Worse, the Earth’s magnetic field varied by latitude. What worked off Rhode Island failed in the waters near Truk or the Solomons.
When crews disabled the magnetic function and relied on direct hits, they found that the contact exploder failed just as often. The firing pin would strike, bend, and shear off without setting off the warhead. The torpedo hit, but the warhead just sat there. It became clear the mechanism was never designed to handle high-speed impact.
Daspit wasn’t the first to notice these failures. Reports had been coming in since 1942. Submariners in Australia tested torpedoes against nets and found them running eleven feet deeper than their settings. Rear Admiral Charles Lockwood demanded more testing. He ordered engineers to break the torpedoes down and figure out why they didn’t work. The results were infuriating.
The depth sensor was mounted in a location that misread the water pressure. As the torpedo moved, it created a false low-pressure pocket around its hull. That tricked the mechanism into believing it was too shallow. It adjusted downward. What the testing lab believed was precision engineering was in fact a consistent misreading caused by basic physics.
The magnetic exploder, praised for its innovation, turned out to be dangerously inconsistent. It often triggered too early or not at all. Sometimes it exploded just from changes in heading or water temperature. It was especially unreliable near the equator, where the magnetic field wasn’t strong enough to trigger the sensors properly. The Navy had tested it near Newport, Rhode Island, where conditions were ideal. No one had bothered to see if it worked in combat zones.
The contact exploder suffered from a different problem. As torpedo speed increased, so did the force of impact. The firing pin block, which worked fine at thirty knots, failed at forty-six. It flexed. It cracked. It jammed. A torpedo could strike a Japanese heavy cruiser, square on the beam, and do nothing more than leave a dent.
After Daspit’s patrol, the Navy could no longer look the other way. Lockwood and others demanded that the Mark 6 magnetic exploder be removed from use. They tested the firing pin assembly and replaced it with a stronger aluminum alloy. They repositioned the depth sensors. The torpedo was no longer perfect, but it finally worked.
Once those changes were made, the fleet’s kill rate improved overnight. Submarines began sinking Japanese merchant ships with brutal efficiency. Convoys that had once shrugged off torpedo attacks began to scatter. The offensive power of the American submarine force had been unshackled.
But those improvements came at a cost. For nearly two years, American submariners went into battle with faulty weapons. Some commanders were blamed for failed missions they had no control over. Lives were lost. Opportunities were missed. Frustration boiled over, and only the courage of skippers like Daspit, Morton, and Lockwood finally forced the Navy to face reality.
The story of the Mark 14 torpedo is not just about a broken weapon. It is about what happens when secrecy overrides transparency, when engineering is driven by theory instead of field results, when leadership refuses to listen to those risking their lives. It is a story every branch of the military ought to remember.
The men of the Tinosa did everything right. They closed with the enemy. They lined up the shot. They fired. And again and again, their weapon failed them. But they brought the evidence home. They demanded answers. And because they did, the rest of the war changed course.
They didn’t just fight the enemy. They fought the system that handed them a dud. And in the end, they won.
National Archives and Records Administration. Deck Logs, USS Tinosa (SS-283), July 1943. Record Group 24: Records of the Bureau of Naval Personnel. National Archives at College Park, College Park, MD. Catalog ID: 74816200.
Cohen, David E. “Technical Report: The Mk-XIV Torpedo—Lessons for Today.” Naval History Magazine 6, no. 4 (December 1992). U.S. Naval Institute. https://www.usni.org/magazines/naval-history-magazine/1992/december/technical-report-mk-xiv-torpedo-lessons-today
Naval Underwater Ordnance Station. U.S. Navy Torpedoes Mark 14 and 23 Types, OP 635. March 24, 1945. San Francisco Maritime National Park Association. Accessed October 27, 2025. https://www.maritime.org/doc/torpedo/index.php
David E. Cohen. Technical Report—The Mk-XIV Torpedo: Lessons for Today. Naval Undersea Warfare Center, December 1992. Volume 6, Number 4
Sunil Parmar. “The Great Torpedo Scandal 1941–43.” Naval Submarine League Archive, September 29, 2021. https://archive.navalsubleague.org/1996/the-great-torpedo-scaodal-1941-43
Al Williams. “The Mark 14 Torpedo — When Just About Everything Goes Wrong, Even the Testing.” Hackaday, May 13, 2020. https://hackaday.com/2020/05/13/the-mark-14-torpedo-when-just-about-everything-goes-wrong-even-the-testing/
Mark Carlson. “The U.S. Navy’s Defective Mark 14 Torpedo.” Warfare History Network, April 24, 2020. https://warfarehistorynetwork.com/article/the-defective-mark-14-torpedo/
“Mark 14 Torpedo.” Wikipedia: The Free Encyclopedia. Last modified 2024. https://en.wikipedia.org/wiki/Mark_14_torpedo
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