Hit Or Miss
AT 10:37 ON THE NIGHT OF APRIL 9, 1943, LT. COMDR. John A. Scott of the USS Tunny saw a sight that other submarine commanders only dream of. After tracking a radar contact and carefully maneuvering into position, the Tunny was prowling the surface just in front of a major Japanese Navy convoy off the Caroline Islands. The convoy included one large auxiliary carrier to starboard and two smaller escort carriers in a column to port. Scott’s skillful guidance had placed the Tunny directly in between, giving her a chance to strike a blow like no other.
After diving to periscope depth, the Tunny approached the convoy while continuing to track the two sets of targets. The normal tension during an encounter was magnified by the importance of the quarry and the unique opportunity to strike a pair of blows at one time. A few minutes later Scott and the crew of the Tunny made history by conducting the first nearly simultaneous bow and stern torpedo attack with carriers as targets. Scott fired all four stern tubes from 880 yards at the leading escort carrier and then almost immediately fired all six bow tubes at the larger carrier, just 650 yards away. Sonar reported four thundering explosions from the first salvo and a few minutes later three explosions from the second.
The Tunny sank six Japanese vessels during World War II—but none of them on .the night of April 9. The explosions the crew heard did only minor damage, for the sub’s Mark 14 torpedoes had all gone off before they hit the ships they were aimed at.
A FEW MONTHS LATER, ON August 29, 1943, on his first patrol as captain of the submarine Halibut , Lt. Comdr. Ignatius J. Galantin sighted a Japanese merchantman protected by a destroyer. Maneuvering his submerged vessel, Galantin switched targets from the cargo ship to the destroyer when it became apparent that he couldn’t close on the merchantman. Maintaining the initiative, the Halibut fired three Mark 14 torpedoes from 1,900 yards.
Galantin watched through his periscope as the torpedoes ran right up to the destroyer without detonating. He waited, then fired three more torpedoes down the throat of the charging vessel. They also refused to detonate, and the Halibut was forced to go deep to evade the destroyer. Six duds for six fired—not an auspicious beginning to Galantin’s command. Years later he would write that after watching his torpedoes speed harmlessly toward the destroyer during his first engagement as captain, he never again felt confident when setting up an attack, although he ended the war with seven sinkings.
These attacks point up two very different problems inherent in the Mark 14, the standard torpedo used by submarines for most of World War II. The Mark 14 was an extremely complex piece of machinery that at the start of the war cost more than $10,000 a shot. With a warhead containing 507 pounds of TNT, it could run 4,500 yards at 46 knots or 9,000 yards at the low-power setting of 31.5 knots, which was rarely used. Its workings were designed to keep the 3,000-pound torpedo running at a predetermined depth and to steer it so that the submarine would not have to point directly at the target ship.
Inside the warhead was the secret 92-pound Mark 6-Mod. 1 exploder. It was designed to detonate either on contact with the hull of a ship or on passing through the magnetic field under the ship’s vulnerable keel. The weak underside was the preferred target, since most modern warships were heavily armored near the water line.
When the Mark 14 worked well, it was magnificent. Far too often, though, its hidden flaws undermined the confidence of captains and crews. For many months after Pearl Harbor, submarines were the chief offensive force available to the United States in the Pacific, yet their only weapon was enormously unreliable. To make matters worse, as one problem was identified and corrected, new ones kept coming to the fore.
The earliest problem to crop up, in the very first days after Pearl Harbor, was unreliable depth control. This could be a severe handicap. For example, in December 1941 the Sargo , under Lt. Comdr. Tyrrell D. Jacobs, fired 13 torpedoes for zero hits. Other subs had results nearly as poor. When Rear Adm. Charles A. Lockwood took over as commander of submarines for the Southwest Pacific in May 1942, he immediately set out to investigate the problem of deep-running torpedoes.
During the desperate six months of retreat from the submarine base at Cavite Naval Yard on Manila Bay, there had been no time to investigate reports of torpedo problems, but after moving into his headquarters in Australia, Lockwood set up a simple test to determine the Mark 14’s actual depth performance. In June 1942 a large fishnet was strung across the bay at Albany, Western Australia. The Skipjack fired three unarmed torpedoes, carefully prepared to weigh the same as live ones, from the surface. The first two, set to run at 10 feet, ripped through the net at 25 feet and 18 feet. The third, set at zero feet, passed through the net at 11 feet.
AT FIRST THE BUREAU OF ORD nance thought these results were due to procedural errors rather than a flaw in the torpedo. A second test, modified to overcome BuOrd’s objection, gave the same results. Soon afterward Adm. Ernest King, the Navy’s commander in chief, ordered the bureau to conduct its own test. In August 1942 it finally announced that Mark 14 torpedoes did indeed run an average of 10 feet deeper than set. The reasons were numerous, including poorly designed tests, faulty record-keeping, and improperly calibrated equipment. (One error that seems obvious in retrospect: Warheads used in BuOrd testing had been filled with water instead of explosive so that they could be reused. When the war started, live torpedoes loaded with TNT weighed significantly more.) While the reasons for deep running were complicated, the solution was simple: Submarine crews simply set their torpedoes for 10 feet less than the depth they wanted.
An equally pressing problem was the supply of torpedoes. There simply were not enough available to arm all the Navy’s submarines and ships. On January 30, 1942, for instance, the Sculpin left the temporary submarine base at Surabaya, in the Dutch East Indies, on her second patrol of the war with only 16 torpedoes, 80 percent of her combat load. This scarcity made wasted shots all the more frustrating. And because of the cost, captains had trained before the war using dummy warheads. The first time a captain ordered his crew to fire an actual armed torpedo usually came while he was looking through a periscope at a Japanese target.
At the beginning of the war, about 60 of the newest Mark 14 torpedoes were produced each month. A fleettype submarine could carry 24 torpedoes, and altogether submarines were using an average of 160 of them a month in 1942. With the loss of the Cavite Navy Yard’s more than 230 spare Mark 14s, the running retreat in the Southwest Pacific, and the long distances involved in delivery, every shot had to count. Captains were encouraged to fire just one or two torpedoes at a target, amplifying the effects of unreliable depth settings. But by January 1943 production had outstripped use, and while delivery still caused problems, the stifling shortages of the war’s first year had ended.
AS THE PROBLEMS OF DEPTH AND supply were being solved, a new difficulty emerged. The Tunny ’s experience with premature explosions, it turned out, had not been unique. The Scamp , on the first attack of her first war patrol, in March 1943, saw all three torpedoes detonate early. Two of her next six did the same. Submariners were hearing explosions, even seeing what appeared to be solid hits, but the target ships steamed on as if nothing had happened.
It takes great care to make torpedoes that will explode only when intended. One safety device the Mark 6 exploder relied on was a small propeller on the underside of the warhead that spun as it traveled through the water. After 450 yards, when the torpedo had leveled off at its predetermined depth and on its set course, the spinning propeller would move the detonator into the booster cavity, arming the torpedo. The Mark 6 also had a countermining device to prevent the warhead from detonating because of a nearby explosion. This kept the first torpedo in a spread from setting off the trailing torpedoes. Any water pressure equal to 50 feet or more would act on a diaphragm to lock the firing pin in place. A torpedo equipped with these safety features was supposed to be difficult to detonate. Yet premature explosions increased as the depth-setting problem was solved in mid-1942.
Part of the problem was the secret Mark 6 magnetic exploder, which detonated the warhead when it entered the magnetic field of a ship’s hull. In theory a Mark 14 torpedo with a Mark 6 exploder would detonate anywhere between the water line of a ship and 10 or 15 feet below the keel, allowing for a large margin of error and increasing the odds of a hit. But the magnetic field generated by a metallic hull varies with the latitude. Close to the equator the field spreads out, which is why torpedoes would often detonate 50 feet from a ship.
Rolling seas, as well as surges in the internal power supply to the coils and vacuum tubes that made up the heart of the magnetic detonator, were also sometimes enough to set off the device ahead of schedule. The Mark 6 was a delicate piece of equipment, and field testing in the furnace of war revealed consequences that had never been foreseen in peacetime.
In June 1943 Adm. Chester W. Nimitz, the commander in chief of the Pacific fleet, accepted recommendations from Admirals King and Lockwood (the latter was by then commander of submarines for the Pacific) that the Mark 14’s magnetic exploders be deactivated. Only the contact mode would be used until a more reliable magnetic exploder was developed. In Australia, however, Adm. Ralph Christie—who two decades earlier had led the team that designed the Mark 6 exploder—had taken over Lockwood’s post as commander of submarines for the Southwest Pacific. Admiral Christie had more confidence in the device, and he ordered subs in his theater of operations to keep using magnetic settings in order to maximize the damage from hits. His submarines thus continued to grapple with the problem of premature detonation. In July 1943 the Grouper had a premature detonation that showered it with fragments of its own torpedo. A month later the Silversides had the first two torpedoes of a four-torpedo spread detonate prematurely, thus warning her intended victim, who managed to escape. Not until March 1944, when a new commander of naval forces overruled Christie, were torpedomen of the Southwest Pacific Force allowed to disconnect the magnetic exploders in their warheads. The Navy did not develop a reliable magnetic exploder until after the war was over.
In July 1943 the Tinosa ran up against the last major problem to plague the Mark 14 torpedo and Mark 6 exploder. Patrolling west of Truk, Lt. Comdr. Lawrence R. Daspit sighted Japan’s largest oil tanker, the 19,262-ton Tonan Maru No. 3 , without an escort. Quickly swinging into attack position, Daspit and his crew fired a spread of four torpedoes at an oblique angle from a range of 4,000 yards—not ideal, but the best position the submerged Tinosa could maneuver into. She was rewarded with two solid hits that did little damage. Tonan Maru No. 3 continued on her way and Daspit fired two more torpedoes. They hit and exploded, causing the ship to stop dead and start to settle slowly by the stern.
The tanker was dead in the water with not another vessel in sight. Deck guns on the disabled vessel kept the Tinosa underwater but couldn’t prevent Daspit from maneuvering into ideal attack position. Just 875 yards from the immobilized tanker, Daspit fired a single torpedo to finish her off. There was no explosion, but Daspit, at the periscope, saw a splash where the torpedo should have hit, just as sonar stopped registering the sound of the torpedo’s propellers. The Tinosa fired two more torpedoes. They also refused to detonate.
The first six shots, fired at extreme range and less than ideal angles, had resulted in two solid explosions and a tanker dead in the water. Then three more, at an ideal angle and range, had yielded nothing. The Tinosa had seven torpedoes left. Over the next hour and a half, six of them were removed and checked carefully, but when they were fired, the result was always the same: another dud. With one torpedo left, the Tinosa withdrew and headed to Pearl Harbor. The reaction of Tonan Maru No. 3’s crew was not recorded, but one can imagine their relief when the damaged ship was towed into Truk lagoon.
Back at Pearl Harbor the remaining torpedo was inspected. When no fault could be found in it or the attack set-up, Admiral Lockwood decided to tackle the mystery on-site. At the end of August 1943 he had two live torpedoes fired at the vertical underwater cliffs of Kahoolawe Island. They both detonated, but a third shot failed to do so. The dud torpedo was recovered, and the contact detonation element of its exploder was inspected. The firing pin had been released, but it hadn’t hit the primer cap with enough force to detonate the primer, so the booster charge and ultimately the warhead couldn’t explode. A team of naval officers was assigned to investigate more thoroughly.
LT. COMDR. E. A. JOHNSON, AN ordnance technician loaned from the Commander Service Force, joined with Lt. Comdr. H. A. Pieczentkowski and Comdr. A. H. Taylor to create a setup that could simulate a torpedo hitting the side of a ship. From 90 feet up, using a crane, they dropped a warhead filled with concrete instead of TNT onto a heavy sheet of metal. In the first series of tests, 7 out of 10 warheads were duds. In each case, just as in the Kahoolawe test, the firing pin was released but failed to hit the primer cap with sufficient force.
Surprisingly, when the sheet metal was placed obliquely, simulating a high-angle attack, the glancing blow of a warhead invariably detonated the primer. That had been the downfall for Daspit and the crew of the Tinosa : They were too good. If they had fired another high-angle shot at the Tonan Maru No. 3 , as with the first six torpedoes, they would probably have gotten a detonation and sunk the tanker.
Further testing revealed the trouble: The spring-driven firing pin, which moved at right angles to the axis of the torpedo, was being squeezed by the compression of other parts of the warhead and couldn’t overcome the friction caused by a solid, head-on hit. Within days several solutions were found. The simplest was to pare down the weight of the pin to reduce the friction on its guide studs. The Navy lost no time in putting this finding into practice, and on September 30, 1943, the Barb left Pearl Harbor carrying 20 torpedoes, the first ones to have modified firing pins in their Mark 6 exploders.
With this correction to its contact exploder, the Mark 14 torpedo finally began to live up to its potential. As happens so often with military technology, it took months of combat to reveal and correct flaws that had been overlooked during twenty years of development and inertia. The history of World War II submarining is filled with examples of boldness and heroism by commanders and crews. With modifications the Mark 14 made sure that these brave men would not overcome the Japanese only to be defeated by their own faulty torpedoes.
