What were the problems with U. S. torpedoes?

In perhaps too much detail, here are the problems and the inadequate testing for each of the major issues:

The torpedoes were running too deep:

Early in the war, the captains complained that the torpedoes were going under the targets. They could see the smoke trail disappear when the torpedo had passed under the target. Torpedo Station staff in Newport, RI, dismissed the complaints saying the torpedoes were thoroughly tested and worked. The captains must be missing their targets due to the chaos of battle or maybe they were just poor shots.

This problem continued until Admiral Lockwood, who was in command of the submarines in Fremantle, Australia, at the time, decided to do his own testing. He hired fishermen to provide nets and fired torpedoes through the nets toward the beach. When his crews fired the torpedoes through the nets, the holes were about 12 to 13 feet deeper than they should have been.

 The U. S. was short of torpedoes at the time, and we needed to retrieve them. The shortage of torpedoes was one of the reasons given for not doing testing with live weapons.

This was reported to the torpedo staff in Newport, Rhode Island. Their response was that the test was invalid. Fishing nets would move when hit by a torpedo. Lockwood acknowledged that more tests might need to be done. However, his tests still indicated a problem and Newport needed to identify and solve the issue. Newport finally did more testing with heavier nets and found that the torpedoes actually ran 10 feet too deep.

Part of the issue was that the original testing was measured by a gauge in the torpedo. It had a similar error which made it appear that the torpedo was running at the right depth. It had not been tested in a way that physically measured the actual depth of the weapon. The tests missed the fact that, since the depth sensor was on the curved afterbody of the torpedo, that caused a low-pressure area above that part of the torpedo. This was similar to an aircraft wing. That’s why the torpedo “thought” that it was shallower than it actually was. Another issue was that the test (dummy) warhead did not weigh as much as the live warheads.

In the short term, captains adjusted somewhat by using a shallower setting to make up for the error until this was fixed.

The magnetic exploder didn’t work:

The idea of a magnetic exploder was a good one. In fact, our torpedoes today generally use a version of the device. The intent was to detonate the torpedo under the target. That bypasses the armor plating of major combatant ships (as much as 16 inches on big battleships) and attacks the more vulnerable bottom. The explosion under the target forces the keel of ship (its backbone) to flex upward. Then, as the gasses escape the empty space under the keel, it flexes downward. These stresses were large enough to break the keel. If the explosion breaks the keel of any ship, it will sink.

Unfortunately, the magnetic exploder often did not work as desired. In many cases, the torpedo detonated as soon as it armed at 400 yards. In other cases, it didn’t detonate at all. The torpedo passed under the target and continued on to the end of its run when it sank to the bottom. Most frustratingly, it did appear to work sometimes. It is very hard to diagnose an inconsistent problem.

Many weapons officers tried to diagnose the problems and solve them. For example, they tried to tighten up fittings so that water wouldn’t affect the weapon. Eventually, they asked how the variable magnetic field of the earth affected the detonator. That question went to the Torpedo Station at Newport. Their response was most discouraging. They provided different instructions if the submarines were above 30 degrees north latitude as opposed to between 30 degrees north and 30 degrees south. They added that they didn’t know how the detonator would respond below 30 degrees south because the poles were reversed.

At this point, ADM Lockwood went to Admirals Nimitz and King and was able to get agreement to disable the magnetic exploder and use the contact function instead. However, that didn’t help the submarines operating out of Australia. Nimitz only commanded the forces in the Central Pacific. General MacArthur commanded the forces in the South Pacific. The admiral now in command in Australia had worked on the project to develop the magnetic exploder and he still insisted that it be used. At that point, if a submarine changed operational control, as Pampanito did after her fourth patrol, the rules changed on the way south and then again on the way back north. Changing the exploder settings was no small project. Eventually, the magnetic exploder was disabled everywhere.

It turns out that the production version of the magnetic exploder had not been tested in a live fire exercise. The story goes that the developers had requested an old hulk to be used in a test. The surface Navy had an old destroyer that was to be scrapped. They agreed to the test with one non-negotiable condition. The hulk had to be returned in the same condition in which it was received. That meant that any testing that was done was without a live warhead. The test was deemed successful if the needle on the gauge moved.

Then they discovered problems in the contact exploder:

After the above two problems were resolved, the submarine captains thought they might have reliable torpedoes. Unfortunately, they found a third issue that had been hidden by the first two. They were now reporting that they could hit the target, but the torpedo often wouldn’t explode. They could hear the torpedo hit the target. They could see the splash from the air flask rupturing as it hit the target. But there was no high-order explosion. This resulted in the familiar back and forth between the fleet and the Torpedo Station about who was to blame.

That continued until July, 1943, when the USS Tinosa (SS-283) found an unescorted tanker, converted from a large whaling ship. Tinosa completed an approach and fired four torpedoes with a near perfect setup. One missed forward and one missed aft. This was not unusual when firing a spread. The other two hit the target but did not explode. Tinosa quickly fired two more torpedoes at an oblique angle as the tanker was moving away and hit it in the stern. This time the torpedoes exploded on contact and destroyed the rudder and propeller. Now Tinosa had a large unescorted target that was dead in the water.

Tinosa then set up eight more perfect, 90-degree shots, one at a time, against the target. None exploded. They pulled some of the torpedoes and did a maintenance before firing. They even moved around to the other side of the target to see if that mattered. It didn’t.

The captain of the Tinosa was furious and sent a blistering message to Pearl Harbor outlining what had happened. He let ADM Lockwood know that he was bringing his one remaining torpedo home with him for testing.

When Tinosa arrived at Pearl Harbor, that one torpedo was loaded onto another submarine, the USS Muskellunge (SS-262), to be fired against the island of Kahoolawe. (You can’t miss an island.) The third torpedo fired did not explode. Then a very brave diver by the name of John Kelly went down and attached lines to the unexploded warhead.

Capt. Swede Momsen, who had also developed the Momsen lung for escaping a sunken submarine, led the team in identifying and solving the problem. They found that the 46-knot collision with the target deformed the rails that the firing pin assembly rode on toward the igniters. That caused the assembly to bind and to stop short of the igniters. Worse yet, the failure to explode occurred most often when the submarine had achieved the best shot, 90 degrees to the target. (The failure occurred in 70% of the tests at right angles.) If the torpedo hit the target at an oblique angle, the forces were distributed differently so that the rails didn’t deform as much. This probably explains why Tinosa’s fifth and sixth torpedoes exploded but not the others.

The solution was to redesign the exploder so that it was triggered electrically. But what to do in the meantime? The best temporary solution was to make the firing pin assembly out of lighter weight, but still sturdy, metal. But where could they find such a metal in Hawaii in 1943? It turns out that the best source was propellers from the Japanese planes that were shot down during the attack on Pearl Harbor on December 7, 1941. As a result, submariners found themselves using the metal from the Japanese planes to fix their torpedoes so they could go out and sink Japanese ships, some of which were made from scrap steel that the U. S. sold to Japan in the 1930s.

By the way, this exploder had been used for years with torpedoes that ran at 30 knots. However, it had never been tested at 46 knots where the forces were essentially doubled. Another temporary solution to the problem might have been to use the Mark 14 torpedoes at low speed.

Circular runs:

Reports were that, during the course of the war, there were as many as 23 circular runs of our torpedoes. Either the gyroscopes were installed incorrectly or, more likely, they failed. It was also possible that the rudders jammed, forcing the torpedo to run in a large circle. In most cases, the boat was able to dive below the torpedo or turn away from it.

However, at least two U. S. submarines were lost to their own torpedoes. The first was the USS Tullibee (SS-284) in March of 1944. The other was the USS Tang (SS-306) in October of that same year. There were a few other boats whose loss has never been explained. They could have been lost to mines, to crew errors, to mechanical failures or to circular runs. We only know the cause of the losses of the Tullibee and the Tang because there were a few survivors from those sinkings.