Mark XIV Torpedo file photo [31415]

Mark XIV Torpedo

Country of OriginUnited States
Diameter533.000 mm
Length6.250 m
Weight1400.000 kg
Range3.657 km
MachineryWet-heater combustion steam turbine with compressed air tank
Explosive Charge230kg TNT or 292kg TPX


ww2dbaseThe Mark XIV torpedo (or interchangeably, the Mark 14 torpedo) was the United States Navy's standard torpedo for fleet submarines throughout World War II. Design work started in Jan 1931 as a replacement for the Mark 10 which had been in service since World War I. Although the same diameter as the Mark 10, the Mark 14 was longer and therefore incompatible with the shorter tubes of the older World War I-era S-class submarines.

Several things drove the need for a new design. By the 1930s, many new warships were fast enough to simply outrun the Mark 10. Newer warships were also being built with armor belts able to withstand the blast of torpedoes like the Mark 10. With the newer armor belts, it was believed that exploding a torpedo underneath a ship to effectively break its back would be more effective than trying to blow a hole in its armor. To these ends, the Mark 14 was conceived as a faster torpedo, with a more powerful warhead, that would explode beneath a ship without ever striking it.

The added speed came from over-revving a fairly typical torpedo wet-heater steam turbine motor. Powering the motor meant larger fuel and air cells, which is what accounted for much of the torpedo's extra length. The more powerful warhead again added a little to the torpedo's length and also to the overall weight. The new warhead benefited from a more powerful but expensive explosive designed by the British called "Torpedo Explosive," or Torpex. Because of its expense, Torpex was initially set aside only for high priority uses like in torpedoes. As time progressed, use of Torpex expanded well beyond just torpedoes but this is where it got its start in the American arsenal.

The third priority, getting the torpedo to explode under the ship, was a harder challenge. To accomplish this, the Mark 14 would be fitted with the Mark 6 exploder (most ordnance people would call this a fuze or a detonator but in torpedoes and torpedoes only, they were called exploders). The Mark 6 exploder was designed in the 1920s to be a combination magnetic/contact exploder. The theory was that when a torpedo ran under a ship, the exploder would sense the magnetic influences of the ship's steel and set off the torpedo beneath the ship. If it could be accomplished, this would be a proximity fuze in a true sense and there was no question that this would be a more lethal attack against any ship. The problem with the magnetic influence exploders was that they were tested so minimally that it is almost true to say they were never tested at all. On 26 May 1926 off Newport, Rhode Island, two torpedoes fitted with predecessors of Mark 6 magnetic influence exploders were fired at the hulk of Submarine L-8. One passed under the target without exploding and the other performed as expected, blowing the old sub in two. These tests, with a 50% failure rate, were the only live-fire tests of magnetic influence exploders by the United States in the entire fifteen years between development and World War II.

As for the contact exploder portion of the Mark 6, that had some problems too. The earliest contact exploders involved a simple firing pin sticking out the nose of a torpedo or artillery shell that was held in place by a much weaker shear pin. When the device struck a solid object, the firing pin broke the shear pin, struck a percussion cap, and set off the main charge. Simple, and it worked. The Mark 6, however, used an overly complicated design first seen in the Mark 3 exploder that, among other things, aligned an internal firing pin at a right angle to the torpedo's direction of motion. The Mark 3 exploders of World War I suffered from a problem where the force of impact often drove a firing pin sideways within its guides in a way that bound the pin in place before it could set off the charge. This was resolved by installing a stronger spring to send the firing pin on its way.

The Torpedo Scandal
Several factors led to the Mark 14 torpedo arriving at the center of what would become known as the United States Navy's Torpedo Scandal of World War II. The first factor was the lack of adequate or realistic testing. In the Depression economy of the period, torpedoes were tremendously expensive. In 1931 when a new car cost $700, the Mark 14 torpedo cost more than $10,000, the equivalent of $180,000 in 2021. The torpedo also suffered from a very low production rate that was crippled by provincial politics that kept all production in New England at the understaffed Naval Torpedo Factory in Newport, Rhode Island. Due to the complexities of the Mark 14 and the demand on the factory to also build other torpedo types, the Mark 14 production rate for 1937 was fewer than two devices per day. Due to the scarcity and the high cost, the United States Navy's Bureau of Ordnance (BuOrd) developed impractical testing procedures that focused more on safeguarding the practice torpedoes than in testing the weapon's true effectiveness. The same frugality prevented submarine commanders from noticing the torpedo's defects because BuOrd strictly prohibited any training with actual, functioning torpedoes. When the United States entered World War II in 1941, the overall number of torpedoes in the Navy's inventory was in the few-hundreds, with many of those being the older Mark 10. Further, 233 of the total number was lost at the outset when they were abandoned at Cavite in the Philippines.

The next contributing factor did not so much contribute directly to the Torpedo Scandal as it clouded the issues from being clearly seen. All through the 1920s and 1930s, the Navy's mission for the submarine service was as a discrete scouting force that cautiously operated on the edges of the battleship fleet. This mission tended to reward cautious and prudent submarine commanders. Navy leaders knew well that Japan was their most likely opponent in the next war and they clearly understood Japan's strategic vulnerability to blockade, but they were unable to follow the logical implications of this because in the 1920s and 1930s, promoting the use of submarines against merchant shipping would have put them squarely at odds with both domestic and international policy makers. Nevertheless, on 7 Dec 1941, five hours after the Japanese attacked Pearl Harbor, Admiral Harold Stark issued broad orders throughout the fleet to immediately institute unrestricted warfare on all Japanese shipping. For the submarine fleet, this would require bold and daring tactics and meant a paradigm-shift within the service that few were prepared for. This sudden adjustment created enough self-inflicted internal turmoil that trivialities like defective torpedoes went unnoticed for too long.

Also to blame for masking the problem for too long was the Navy's organizational structure and some parochial attitudes embedded within it. Beginning just before World War I, the Navy developed two completely new areas of operations to supplement the surface fleet: aviation and submarines. Naval Aviation benefited from having a dedicated advocate in Washington in the Bureau of Aeronautics (BuAer) but the submarine fleet had no such spokesman. As World War II opened, the submarine command structure was broken into three segments, the Atlantic Fleet, the Pacific Fleet, and the Southwest Pacific Fleet. Each of the co-equal submarine commanders was located in his respective region subordinate to the regional fleet commander. The submarine force had no oversight in Washington to speak for the entire submarine community; and with no central submarine commander, there was also no one to guarantee that all three submarine fleets shared information or coordinated their actions. What's more, the submarine service did not develop the Mark 14 torpedo, it was developed entirely by the Navy's Bureau of Ordnance (BuOrd) in strict secrecy. BuOrd held a great deal of sway in Washington Navy circles and few were inclined to challenge them. BuOrd definitely saw the Mark 14 as belonging to them and not to the submarine service. The result was that once the submarine fleet sorted out their doctrinal paradigm-shift and started noticing problems with the torpedoes and with no one in Washington designated to champion their case, they got nothing but resistance from BuOrd.

Beginning with USS Seawolf on 14 Dec 1941, barely a week after the Pearl Harbor Attack, submarine commanders started reporting Mark 14 torpedoes were running deeper than the indicated depth setting, too deep to trigger the magnetic exploders. Complaints worked their way up the ladder but responses from BuOrd were consistent in their blame of the submarine commanders for faulty tactics and claims there was nothing wrong with the torpedoes. Accompanying those dismissive responses were clear orders from BuOrd reiterating that the expensive and short-supplied torpedoes were not to be used in any field-testing.

In Australia, the newly appointed commander of submarines for the Southwest Pacific Area, Rear Admiral Charles Lockwood, recognized that it was far more expensive to send submarine crews into combat with faulty weapons so, against BuOrd orders, he commissioned his own depth tests in King George Sound in southern Australia. On 20 Jun 1942, USS Skipjack fired a Mark 14 torpedo with an exercise head at a net from a distance of 850 yards. The torpedo's depth setting was 10 feet but it went through the net at 25 feet. More tests determined the torpedoes ran an average 11 feet deeper than their depth settings. Test shots through multiple nets set at intervals also revealed the torpedoes were not running at constant depths but were porpoising. Results were sent to BuOrd who responded with their usual refusal to see flaws in "their" torpedo. Chief of Naval Operations Admiral Ernest King, however, stuck up for his sailors. He imposed upon BuOrd an abrupt paradigm-shift of their own and directed them to look at the problem more inwardly. By 1 Aug 1942, after actually conducting some tests, BuOrd reluctantly conceded the Mark 14 torpedo tended to run deep and that its depth-control mechanism may have been improperly designed and tested. By this point in the war, 800 Mark 14 torpedoes had already been fired in combat.

The problem turned out to be the position of the opening in the torpedo body that connected outside seawater with the pressure sensor. This port was near the fins where the torpedo body tapers. This arrangement worked perfectly when BuOrd lowered torpedoes into tanks of still water but when the torpedo was running at its top speed of 46 knots (53 mph or 85 kph), this became an area of low pressure that falsely indicated a shallower depth and so the torpedo was guided downward. This was actually corrected by BuOrd fairly quickly after Admiral King's directive and the location of the port was repositioned.

This was an improvement but not a fix. Also, by then the submarine commanders had found their own fix by simply setting the depth control to zero. This gave them very different but still unsatisfactory results. The torpedoes' running depth was improved but often these torpedoes exploded harmlessly short of the targets; known as "prematures." The first reported premature was from the USS Sargo and also just a week after the Pearl Harbor Attack. Believing the torpedo problems had been solved, BuOrd, and even Lockwood, were hesitant to look again for design flaws in the Mark 14. But submarine commanders kept reporting the same experiences with amazing consistency, so it could not be ignored. The premature detonation problem was thought to be an issue with the magnetic exploder but the precise reasons were not well understood. It turns out that the earth's magnetic field differs greatly depending where on Earth it is measured. The Mark 6 exploders were only minimally tested and all of those tests took place near Newport, Rhode Island. The earth's magnetic influences in the western Pacific were quite different and the targets were routinely setting off the magnetic exploders 50-75 yards before the torpedoes reached them. These explosions were close enough to sometimes be seen through a periscope as hits without effect, but Magic code-breaking intercepts showed the Japanese ships were reporting these as prematures. Submarine commanders paid little attention to the nuances of magnetic fields, they just knew the devices did not work and there was growing interest to simply disable the magnetic exploders. Admiral Lockwood, now commander of submarines in the Pacific Area, endorsed Admiral Nimitz' order to disable the magnetic influence feature but Lockwood's replacement in the Southwest Pacific Area, Rear Admiral Ralph Christie, saw it differently. Before taking command of submarines in Australia, Christie had spent many years at BuOrd and he was, in fact, leader of the team that developed the Mark 6 exploder (ironically, it had been Christie who proposed testing the exploders at different latitudes to see if magnetic influences were the same throughout the world). By 1942, however, Christie had great faith in the device and he issued strict standing orders that no part of it would be disabled or modified.

Reports from submarine commanders began reflecting fewer torpedoes running too deep and fewer prematures, but now they were full of reports of solid hits with no explosions - duds. The Mark 14 torpedoes were now dependent on the contact exploders with the laterally mounted firing pins. When the older Mark 6 exploders were installed in the newer Mark 14 torpedoes, BuOrd did not fully appreciate that the new heavier and faster torpedoes generated enormously greater internal forces when striking a ship and those forces might bind the firing pins as they had before. Because the earlier problems were all addressed at BuOrd under the strictest secrecy, neither Lockwood nor the submarine commanders knew anything about them or how they had been addressed. Ironically again, the best person outside BuOrd to understand this particular issue was Christie, but he was having a hard time seeing any problems with the exploder. Lockwood had had some success testing torpedoes on his own authority once before, so he ordered some tests of the contact exploder. Live torpedoes were fired at underwater cliffs in Hawaii and dummy warheads were dropped from cranes at the Pearl Harbor submarine base. The subsequent examinations revealed deformation of the entire firing pin mechanism sufficient to keep the pin from moving at all or causing it to miss the percussion cap. Either way, the result was a dud. Without bothering to consult BuOrd, Lockwood authorized re-working the firing pins to machine away a large portion of their weight and he also allowed fabrication of lighter aluminum firing pins. Both of these modifications gave better test results and soon found their way into operational torpedoes. This was Oct 1943 when war was half over and the tide had already begun to turn in the Pacific. Only then did the United States Navy's submarine force go to war with an effective primary weapon - but only the submarines in the Pacific Area under Lockwood.

Since it was not uncommon for a submarine to start a war patrol from Pearl Harbor, Hawaii and end it in Fremantle, Australia, submarine commanders had to juggle conflicting orders with respect to what parts of their torpedoes they could or could not make adjustments to. Since the reverse course was also true and submarines came back to the Hawaiian area, frustrated commanders brought word of these conflicts to Lockwood. Lockwood's immediate superior was Pacific Fleet commander Admiral Chester Nimitz, an old submarine sailor himself who may or may not have had a part in what happened next. In Nov 1943, Vice Admiral Thomas Kincaid arrived in Australia from Hawaii as the new commander of the Southwest Pacific Area and Christie's new immediate superior. Kincaid promptly gave Christie a direct order to have the Mark 6 exploders deactivated in all combat commands. Christie complied but, according to the entry in his personal diary for that day, he took this as a tremendous personal defeat.

While many of the problems were largely corrected in the field without extensive collaboration with BuOrd, BuOrd was complying with Admiral King's directive and making their own studies that reached many of the same conclusions. With respect to the firing pin problems, BuOrd solicited advice from none other than Albert Einstein who wrote a letter, complete with hand-drawn diagrams, describing the exponential increases in the internal forces as torpedo impacts approach right-angles to the targets versus more oblique approaches. Dr. Einstein's science was, of course, flawless and he suggested a solution along very different lines, but it came after the field-modified firing pins had already addressed the problem satisfactorily. In early 1944, near the end of BuOrd's corrective inquiries, Bureau Chief Rear Admiral William "Spike" Blandy issued this revealing and uncharacteristic written directive:

"Even with the relatively meager funds available in the time of peace, much of the work now being done after more than a year and a half of war could, and should, have been accomplished years ago. That the work was not accomplished during peace, or earlier during the war, or so far as the Bureau's records disclose that no one either at the Bureau or at Newport apparently questioned the inadequacy of the design without such tests, shows a lack of practical appreciation of the problems involved which is incompatible with the Bureau's high standards and reflects discredit upon both the Bureau of Ordnance and the Naval Torpedo Station, Newport. The Chief of the Bureau therefore directs that as a matter of permanent policy, no service torpedo device ever be adopted as standard until it has been tested under conditions simulating as nearly as possible those which will be encountered in battle."

Not all Mark 14 torpedo troubles were resolved, however. Besides the depth control error, the poorly tested magnetic exploder, and contact exploder failures, the Mark 14 suffered from occasional and unexplained circular runs that lethally threatened the submarine that fired it. This was not a problem unique to the Mark 14, however; all torpedo models from all nations suffered from this issue to some degree or another. The reasons behind these failures in US torpedoes were never conclusively determined but prevailing theories suggest not all were caused by the same thing. Suspicions focused on faulty gyros and/or defective linkages between the gyros and the rudders. Among United States submarines in World War II, there are thought to have been a total of 30 cases of circular running torpedoes, two of which struck and sank the submarines that launched them; USS Tang by an electric Mark 18 torpedo and USS Tullibee by a Mark 14. Of these thirty, 22 involved Mark 14 torpedoes (73%), but this high proportion is deceptive. Far more Mark 14s were fired from submarines than all other types combined, so 22 out of 30 is about the same ratio as Mark 14s fired compared to the total number of torpedoes fired. Statistically speaking, 30 circular runs out of all 3,200 torpedoes of all types fired from American submarines in World War II is an exceedingly small number (0.9%), but the catastrophic potential in these failures continue to have "circular runs" listed among Mark 14's problems in the relevant literature.

So the success of the Mark 14 torpedo was hampered by four main problems: depth control, prematures, duds, and circular runs. Delays in quickly correcting these problems were exacerbated by the United States Navy's inability to get out of its own way at several levels. To be fair, the Mark 14 cannot be blamed for the Navy's intransience, the circular runs that plagued all torpedo designs more or less equally, or the problems that were more correctly attributed to the Mark 6 exploder. That leaves just the depth control problem. This issue was clearly due to a design problem with the Mark 14 but would have been quickly discovered in early testing, had there been any.

On the other side of the ledger, the Mark 14 torpedo remained the primary weapon for the United States submarine fleet throughout the war with over 13,000 built. It is credited with sinking over 4-million tons of Japanese shipping. While comprising only 2% of the United States Navy's battle force, submarines accounted for 55% of the shipping sunk by United States forces in World War II.

United States Navy
Naval Postgraduate School, Monterey, California; Mark XIV Torpedo Case Study by David Matthews, 2011
Strategy Bridge - Michael J. Hennelly, 8 Feb 2018
Defense Media Network
Military History Online
Drachinifel Naval Historiographer YouTube Channel; The Mark 14 Torpedo - Failure is Like Onions, Feb 2020
The History Channel
The Submarine Review; Oct 1996
Naval Weapons of the World (
Hackaday Blog
Warfare History Network
The National Interest
The Pacific War Online Encyclopedia
San Francisco Maritime Museum
Julius Augustus Furer: Administration of the Navy Department in World War II
Stephen Moore: Presumed Lost: The Incredible Ordeal of America's Submarine POWs during the Pacific War
Weapons and Warfare
United States National Oceanic and Atmospheric Administration
We Are the Mighty
War History Online
Council of American Ambassadors


Last Major Revision: Sep 2021

Mark XIV Torpedo Interactive Map


Cutaway diagram of the Mark XIV torpedo, 1940s.Aerial view of Goat Island in Narragansett Bay and within the City of Newport, Rhode Island, United States which became home to the United States Navy’s Bureau of Ordnance Naval Torpedo Factory in 1869.United States Navy photograph showing the size comparison between the Mark XIV submarine torpedo (top) and the Mark XIII aerial torpedo.Seven United States Navy officers and one Chief Petty Officer pose with the station’s first Mark XIV torpedo at the Naval Torpedo Station at Keyport, Washington, United States, 1943.
See all 9 photographs of Mark XIV Torpedo

Mark XIV Timeline

14 Dec 1941 Six days after the Japanese attack on Pearl Harbor, Hawaii, two separate US submarine attacks were crippled by two different flaws in the Mark XIV torpedo. The USS Seawolf on the north shore of Luzon in the Philippines fired torpedoes that ran too deep and USS Sargo off the coast of Cam Ranh Bay, Indochina (Vietnam) experienced one torpedo that exploded prematurely.
20 Jun 1942 Acting on orders from US Commander of Submarines Southwest Pacific Area Rear Admiral Charles Lockwood, and against standing orders from the Bureau of Ordnance, submarine USS Skipjack fired one Mark XIV torpedo with an exercise head from a distance of 850 yards at a net hanging in the water. The torpedo’s depth setting was 10 feet but the torpedo went through the net at a depth of 25 feet.
31 Aug 1943 Under the direction of the irascible Commander Charles "Swede" Momsen and acting on orders from US Commander of Submarines Pacific Area Rear Admiral Charles Lockwood, submarine USS Muskellunge fired three Mark XIV torpedoes at the underwater cliffs of Kahoolawe Island, Hawaii to test the torpedo’s contact exploders. Two exploded and one did not. Momsen himself dove on the damaged but unexploded torpedo and rigged it for recovery. He then delicately dismantled the exploder device and revealed the design defects that had caused it to fail.
4 Jan 1944 Physicist Albert Einstein sent a two-page letter to the United States Navy’s Bureau of Ordnance describing the exponentially increasing forces created a torpedo strikes a target at a right angle versus more oblique approaches.

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Cutaway diagram of the Mark XIV torpedo, 1940s.
See all 9 photographs of Mark XIV Torpedo

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