Torpedoes

According to the Merriam-Webster Dictionary, a torpedo is “a weapon for destroying ships by rupturing their hulls below the waterline: such as a submarine mine or a thin cylindrical self-propelled underwater projectile.”

In 1864, when Admiral Farragut said something along the lines of “Damn the torpedoes, Captain Drayton, go ahead” he was referring to what we think of as a minefield. In those days, a torpedo referred to any underwater weapon. However, in 1866 Robert Whitehead developed a motorized torpedo. This was the prototype of what we think of as a torpedo today, the last part of the definition above. What Admiral Farragut was concerned about is what we today call mines. We now just call the motorized torpedo a torpedo.

Merriam-Wester defines a missile as an object (such as a weapon) thrown or projected usually so as to strike something at a distance - stones, artillery shells, bullets, and rockets are missiles. Common usage indicates that missiles travel through the air, like the artillery shells or rockets. Although a torpedo could fit under the above definition, it is not normally considered a missile. 

However, there are missiles that can deliver a torpedo through the air to the water near a target. To further cloud the question, modern submarines can launch both advanced capability torpedoes and Tomahawk missiles from the same torpedo tubes. The newest submarines often have vertical tubes to store and launch Tomahawks and other missiles. They wouldn’t always need to launch missiles through the horizontal torpedo tubes.

Torpedoes can be classified by method of propulsion and whether they were homing or aimed. During WW2, great advances were made in torpedo design. However, they were still rather basic compared to current weapons.

The most common methods of propulsion were by electric battery, steam from fossil fuels, or diesel engines. The British used diesel engines. We will focus here on American torpedoes which were either steam driven or were battery-driven electric weapons.

Electric torpedo – a torpedo that was powered by a battery and an electric motor. The torpedo seen on the USS Pampanito (SS-383) museum in the forward torpedo room on the starboard side was electric.

Steam torpedo – a torpedo that had a steam engine. Steam was produced with a volatile fuel - generally alcohol – along with air and pure water in an internal combustion chamber. The steam was then directed into a turbine to drive the propellers. Steam was not added to the torpedo prior to firing.  It was generated inside the torpedo upon firing.

Aimed torpedo – the torpedo was given a final course to collide with a target. Regardless of what the target did, the torpedo was not designed to change course.

Homing torpedo – the torpedo would search for the target, typically using a sonar. It would be aimed towards the target and would then respond to changes in course or speed by the target.

The first thing that was needed was to develop a firing solution. Therefore, it would help to explain that process first.

The captain and crew had to determine where the target was, where it was going and how fast it was moving. To do that, they used the Torpedo Data Computer, known as the TDC, in the conning tower as an aid.

The TDC was a large electromechanical computer that was developed in the 1930s. It was the size of a large American refrigerator and weighed about 1,500 pounds - somewhat larger than your laptop or tablet. The TDC was developed from a computer that controlled the big guns on surface ships. It had no software and did only the one thing –compute the final course for the torpedo so that it would collide with the target. It used gears, wheels, motors and servomotors. It accounted for the turning characteristics of two different torpedoes, one that ran at either of two speeds and the other that ran at a third speed. (It was clearly designed by a genius.)

The British, Germans and Japanese had similar devices that calculated the course for a given point in time. The TDC, however, provided a running solution. It updated itself constantly, based on the parameters that were entered. Therefore, if the approach officer had to wait a minute or so before firing, as long as there were no changes to the manual input parameters, there was no need to recalculate. The other machines had to recalculate in such a situation.

The target solution was developed using observations of the target and the TDC. The course and speed of the submarine were fed into the machine automatically, from the gyrocompass and the speed log. The approach officer, usually the captain but perhaps the XO, would sight the periscope on the target for the bearing and use a range finder to determine the distance to it. Those values could then be transmitted from the periscope, or from the Target Bearing Transmitter (TBT) on the bridge, to the TDC.

The crew still needed to determine the course and speed of the target. The course was estimated by the “angle on the bow” of the target. This provided from an observation by the approach officer. A zero angle on the bow means the target was headed directly toward the boat. A 90-degree angle on the bow, port or starboard, meant the target’s course was at a perpendicular angle and probably was starting to move away from the boat. A 180-degree angle on the bow means the target was headed directly away from the sub. This angle changed continually as the attack developed. Approach officers practiced determining the angle on the bow of the target and usually were very good at it.

The remaining parameter was the speed of the target. If the target was a merchant ship, most speeds in WW2 would be around 8 to 10 knots. That made it easier to come up with an initial estimate. However, combatant ships such as destroyers or cruisers could be steaming at anything from 10 to 30 knots. To get an initial estimate of the target’s speed, the approach officer checked to see if the target had “a bone in his teeth.” He looked to see if there was a tall white wake (the bone) at the bow of the target. If so, it was sailing at a higher speed. Late in the war, as sonar improved, the crew might have been able to get a “blade count” on ships. They could actually count the revolutions of the target’s propellors. Once they had that and identified the type of ship, they could determine the speed.

The TDC operator updated the estimates with each observation. When the approach officer wanted to make another observation, the periscope was brought up on the bearing where the TDC estimated the target to be. If the target was on that bearing, that meant that they likely had a good working estimate. However, if the target was at a different bearing, they needed to adjust. If, for example, the target was ahead of where it was expected to be, was it closer than estimated or going faster than estimated? Either could be true. If, on the other hand, the target was where it was expected to be for a few successive observations, it was probable that the TDC had a good solution.

All the time that the TDC was running during the approach, it was adjusting the gyroscopes in the torpedoes. This was done via servomotors. The TDC sent the signal from the output side of the machine to the small boxes on the side of each torpedo tube. That caused the spindle into the torpedo to set a new final course into the gyroscope. All of the torpedoes in the tubes in the torpedo room would be updated with the current course calculation.

Once the approach officer had a good solution and the target was in the optimum location, it was time to launch the torpedo(es). To fire a torpedo, first the tube had been flooded and pressurized to match sea pressure. Then the outer door was opened. This happened before the target was in firing range.

When the order was given to fire the torpedo, it would be fired electrically from the conning tower. There was a panel that allowed the operator to select the desired tube in the forward torpedo room or the after room. The panel provided status information such as whether the outer door was open and whether the gyroscope in the tube matched the setting from the TDC. When all was ready, there were two firing keys (actually plungers), one for the forward tubes and one for the after group. The torpedoes could also be fired from the torpedo rooms in case there were problems with the firing keys.

The torpedo would be launched with a small blast of air at 300 PSI. This would get the torpedo moving and the steam engine or electric motor would start right away. It would then swim the rest of the way out of the tube and speed towards the target. The launching air was then captured by a series of poppet valves above the tubes and brought back into the boat. They did not want a large bubble of air to escape from the tube to give away their position.

The torpedo normally dropped down about 30 feet in depth until it got up to speed. Then it recovered to the desired depth. It would run straight out of the tube for about 100 yards and then would turn to the course stored in the internal gyroscope. With luck it would continue on that course until it hit the target and exploded.

The TDC could be used to help plan the attack. One of the features of the output side of the TDC was that the operator could put in the desired spread, in degrees, of the torpedoes. Another feature was that the operator could determine the optimal course for the submarine so that the torpedo did not need to make the turn. It could indicate the course for a zero-angle shot. Torpedoes could turn up to 80 degrees off the firing axis, but large turns increased the chance of errors. If there were only the one target, eliminating the need for the torpedo to make a turn improved the odds of a successful firing.

Generally, the boat needed to be at medium speed or less to fire a torpedo. High surface speeds could cause damage to the torpedo tube outer doors. Submerged speed was rarely an issue since the boat wouldn’t go over 9 or 9.5 knots (10 or 11 mph).

At the beginning of the war, we still had stocks of the Mark 10 torpedo from WW1.  However, the Mark 14 steam torpedo was the primary submarine weapon early in the war. The Mark 18 was an electric torpedo. The Mark 23 torpedo was the same as the Mark 14, but with only one -speed setting. The Mark 27 was a small defensive, electrical weapon. The Mark 28 was an electric, homing torpedo but was not ready until very late in the war. Details on each of these torpedoes follow.

The Mark 10 torpedo:

The Mark 10 torpedo was a steam torpedo that was aimed. It had been developed at the time of WW1. It had been superseded by the Mark 14 by the beginning of the war, but there was still a limited supply available. The Mark 10s were intended primarily for the old R and S class boats. However, the Mark 10 was less problematic and more reliable than the Mark 14 and was sometimes preferred even in the newer boats.

A key difference between the older and newer submarines was in setting the gyroscope for the final course of the torpedo. In the older submarines, the mechanism to set the gyroscope was on the outside of the torpedo tube. In the newer submarines, including the Gato, Balao and Tench boats, there was a spindle that was inserted through the tube and into the torpedo to set the gyroscope. Newer boats using the Mark 10 would have to compensate for the difference.

The Mark 14 torpedo:

There is a sample of the Mark 14 torpedo on the port (left) side of the forward torpedo room on the Pampanito. The after end of the torpedo has cutaways so you can see the combustion chamber, differential, a lubricating tank, etc. The Mark 14 torpedo was designed before WW2 started and was the primary weapon for most of our submarines for the first half of the war. The torpedo weighed just over 3,200 pounds including the warhead of about 640-pounds.

This torpedo had two speed settings: 46 knots (about 53 MPH) or 30 knots (about 35 MPH.)The range was a bit over two nautical miles at high speed and a bit under four miles at low speed. The captains would very rarely fire at a target that was four miles away. The typical firing range was 750 to 1,500 yards, although ranges of up to 3,000 yards were not unheard of. However, as always, the further away the target was, the less likely that the submarine would hit it.

Not only was it geometrically harder to hit something at four nautical miles, but the target was very likely to zig before the torpedoes got there. Most zigzag plans had legs of ten minutes or less. The time needed to determine the target’s new course after a turn and then for the torpedo to arrive could easily exceed the time that the target was on that new course.

The Mark 14 was a steam torpedo, but it didn’t have a traditional boiler and they didn’t load steam into it. Instead, the torpedo carried alcohol fuel, pure water and an air flask charged to 2,800 PSI. You can see the combustion chamber in the smaller cutaway in the torpedo on the Pampanito. When the torpedo was fired, the engine started right away. Air was sent to the combustion chamber at a reduced pressure of 250 PSI. An alcohol spray was added. The pressurized air flow triggered an igniter and resulted in a flame with the 250 pounds of pressure behind it. (Perhaps similar to a cutting torch.) To that they added a fine water spray that flashed to steam. Wet heat (steam) was much more efficient than dry heat. This steam powered a turbine that was above and just aft of the combustion chamber. (The actual turbine is difficult to see in Pampanito’s Mark 14 torpedo.) That turbine then drove the counter-rotating propellors via the differential, and the exhaust gasses added more speed.

The fuel and water tanks were positioned just forward of the combustion chamber. The rest of the forward section of the torpedo, up to where the warhead was attached, was the air flask. The tank that you see near the differential was for a lubricant.

The advantage of the Mark 14 was the higher speed and the added range at lower speed. The disadvantage was that it left a trail of bubbles and thin smoke behind it. This usually wasn’t enough to allow the target to spot the wake in time to turn, but it did alert escorts to where the submarine was when it fired the torpedo(es).

The Mark 14 was not a homing torpedo, but was aimed. There was an internal gyroscope that stored the final course of the torpedo given to it from the Torpedo Data Computer (TDC) in the conning tower. The aiming process was discussed above.

The standard Mark 14 torpedo was too long to be used in the old R and R boats. A modified version, still a Mark 14,  was developed that was shorter so it would fit in the torpedo tubes of those older boats.

The Mark 18 torpedo:

The Mark 18 was an electric torpedo. A sample of the Mark 18 on the Pampanito is on the starboard (right) side of the forward torpedo room. Most of the side of this torpedo is cut away and covered with plexiglass. This torpedo weighed about 3,000 pounds including the 600-pound warhead.

This torpedo was reverse engineered (copied most of the design) from a captured German electric. These were designed and built by Westinghouse, and didn’t reach the fleet until late 1943 or early 1944. The advantage of this torpedo was that it didn’t leave a trail of bubbles and smoke. However, it was slower than the Mark 14 steam torpedo. The Mark 18 had just the one speed setting of about 28 knots. The range was about two miles.

The forward part of the torpedo, behind the warhead, carried the lead-acid batteries that powered the torpedo. On the Pampanito, just behind the batteries, you can see the motor that drove the counter-rotating propellors. The air flasks that are visible in the afterbody would power up the gyroscope used to aim the weapon. In later models, the gyroscope was spun up electrically.

When the torpedo was fired, the engine started right away. As is the case with electric cars, the electric motor gets up to full speed very quickly. For these torpedoes, the sudden increase in speed was initially a problem. The rapid acceleration in the tube caused the torpedo to hit the sides of the tube and be damaged. Additional guides solved that problem.

The Mark 18 was easier and quicker to build. Since there was no trail of bubbles and smoke, the target wouldn’t usually be able to see it coming and was less likely to evade it. The lack of a bubble trail also meant that the enemy didn’t have a set of pointers showing exactly where the submarine was when it attacked.

The biggest disadvantage of the Mark 18s was that they were slower. The target had more time to change course on routine zigzags. Another disadvantage was that the batteries needed to be recharged periodically and that generally caused some hydrogen to be generated. The hydrogen had to be burned or dissipated safely before it reached explosive levels.

Sources indicate that about two-thirds of all the torpedoes fired in 1944 and 1945 were the Mark 18s. Because there were still reliability issues, this version was removed from service shortly after the war and was replaced by another electric version.

Like the Mark 14, the Mark 18 was an aimed torpedo. There are only examples of the Mark 14 and Mark 18 torpedoes at the Pampanito.

The Mark 23 torpedo:

As noted above, the Mark 23 was the same torpedo as the Mark 14,but with only a high speed setting. Since the low speed setting of the Mark 14 was rarely used in the early days of the war, this new version was developed. However, by the time the Mark 23 reached the fleet, requirements had changed and few were fired. Most were cannibalized for spare parts for the Mark 14. (“Hellions of the Deep” by Robert Gannon, pg. 76 footnote.)

The Mark 27 Cutie torpedo:

The Mark 27 torpedo was a small (short) homing torpedo that we developed late in the war. Submariners called them “cuties” because of the small size. These were defensive torpedoes. The idea was that they would be launched in the direction of an enemy anti-submarine warfare (ASW) ship with the expectation that it would home in on and destroy the propellors and disable the ship. The small warhead was not expected to be enough to sink the attacking ship, but it did indeed do that at times.

The launching submarine was supposed to be at least 150 feet deep to be protected by safeties.

The Mark 27 was developed based on the Mark 24 mine, which was actually a small air-dropped torpedo. The Mark 24 was called a mine to hide its capabilities. The Mark 24 FIDO, as it was named, was actually a homing torpedo designed to be dropped behind a U-boat as it was submerging. The air-dropped Mark 24 torpedo was used to sink 31 German U-boats and six Japanese submarines.

The Mark 28 homing torpedo:

The Mark 28 torpedo was an attempt to create a homing version of the Mark 18 electric. Because it was created late in the war, development and testing were rushed. The Mark 18 was still a noisy torpedo. The design of the Mark 28 was to use the gyroscope aiming process to get the torpedo close enough to the target for the homing device to take over. The lack of thorough testing meant that, once again, captains in combat situations had to do the beta testing to the peril of their own boats and crews.

There isn’t much information available about the Mark 28s since it was soon discontinued. CDR (later to become admiral) Gene Fluckey on the USS Barb (SS-220) had some Mark 28s for his last patrol and they were total failures. His comments: “Later I was informed that the Mark 28 torpedoes had not been tested in shallow water. Tests showed that ships’ propellors emitted both a direct sound path and a strong sound path that reflected or bounced off the bottom at lesser depths. Thus, those we had fired headed for the bottom to bury themselves in the mud or sand, or they failed to start.” {“Thunder Below” by Gene Fluckey, page 408.)

First, a couple definitions. To aim a torpedo is to point it at a target. It would then go directly in the direction where it was aimed. A guided torpedo is one that can be redirected towards the target by remote human control or by onboard sensors after it is fired.

Late in the war, we developed a few homing torpedoes, although with mixed success. The primary difficulty was in overcoming the noise of the torpedo itself in order to find the target. Other noises in the ocean, which had never been measured, would also affect the homing device. The intent was for these torpedoes to be aimed by the TDC and then run on the course stored in the gyroscope until, hopefully, the target noises allowed the homing mechanism to take over.

Most of our WW2 torpedoes were not guided. A few acoustic homing torpedoes were developed during the war. We developed a Mark 27 homing torpedo for submarines as a defensive weapon. Sailors called it a “cutie”. It was small and was just intended to disable the attacking ASW ship – a destroyer, escort, corvette, etc. If it sank the ASW ship, so much the better, but that wasn’t the primary objective.

We also had a Mark 24 Mine (actually a small homing torpedo) that was used by our aircraft to attack and sink U-boats in WW2 in the Atlantic. It was called a FIDO.

However, most of the torpedoes that we used, such as the Mark 14 and Mark 18 that we have in the forward torpedo room, were simply aimed. A target solution was entered into a gyroscope in the torpedo before it was fired. As noted above, these torpedoes would go straight out of the submarine for about 100 yards and then turn on its final course. Then they would go straight. That turn was part of the aiming of the torpedo, not guidance.

The irony was that, at the beginning of the war, the U. S. probably had the best fire control but the worst torpedoes. The common theme was inadequate testing as detailed below. At the beginning of WW2, there were at least four major issues with our torpedoes. Worse yet, it took the U. S. nearly two years to fix most of them so that they could send out crews and boats with fairly reliable torpedoes. In each case, the testing was insufficient or non-existent.

Most of our torpedoes were developed at the Torpedo Station in Newport, Rhode Island. The staff at the Station consistently blamed the skippers for being poor shots in the chaos of battle or for inadequate maintenance. The skippers’ immediate superiors (division or squadron commanders) sided with the torpedo staff. That doesn’t seem to make much sense since those commanders were responsible for training and evaluating the captains. Eventually, ADM Lockwood, commander of submarines in the Central Pacific, began his own testing. He was able to identify the actual problems so they could be fixed. However, in the end, no one was actually held accountable.

NOTE: U-boats experienced many similar problems with their torpedoes although the causes were sometimes different. For example, U. S. torpedoes ran too deep in part because the depth sensor was on the curved afterbody of the torpedo. That created a low-pressure area and the torpedo behaved as though it was too shallow. It then ran deeper, too deep. The German version of the similar problem was caused by a post running through a diaphragm in the pressure sensing area. As the pressure in the boat increased due to firing torpedoes, that increase would leak around the post into the pressure sensor area and the torpedo ran deeper. However, the biggest difference was that Admiral Doenitz believed his captains when they reported problems and he leaned on the manufacturers to get them fixed. When he threatened that heads could roll, it may have been a literal threat.

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.

There was a safety device to keep the warhead on a Mark 14 or Mark 18 from exploding too close to the submarine which could damage the boat. It was an impeller on the front of the torpedo that prevented the torpedo from exploding until it had run about 400 yards. The impellor pulled out a safety screw. (An impeller is a device like a small propellor, but the water moves the impeller, not the other way around.)

After the Tang was lost, more work was done on an anti-circular run (ACR) device which would prevent the torpedo from exploding if it circled back at the submarine.

There was also a safety device to keep the torpedo from going below 100 feet. That is why the submarine was supposed to be at 150 feet or deeper.

No. Captains realized that submarines could attack on the surface at night, when they could hardly be seen. German U-boat captains had learned the same thing much earlier. Sonar won’t find a submarine on the surface because it is lost in all the noise. Radar was needed to find the boats on the surface at night, and the Japanese were slow to provide that equipment to escort ships.

A spread was fired sequentially, usually at seven to ten second intervals. That way, the turbulence from the first torpedoes didn’t have so much effect on the later weapons. This is similar to jet aircraft taking off and for similar reasons.

The torpedoes did not explode based on a timer. The Mark 6 exploder was used for most of the war. It could be configured in either of two ways. However, it wasn’t a quick, easy process to change the configuration. One setting was for a contact exploder, so that it exploded when it hit the target. The other way was to set it to explode when it sensed the magnetic field of the target as the torpedo passed under it. As noted above, the magnetic version of the exploder failed often during the war and eventually was no longer used. The contact configuration was then used all the time, even though there were problems with it that had to be fixed. The magnetic feature was improved after the war and is part of the mechanisms used today.

We know that the boat was supposed to be deeper than 150 feet when using the Mark 27 homing torpedo. There was a safety mechanism to protect the boat if it was at that depth. However, that was for a defensive weapon. Most attacks required visual bearings and ranges. The boat would be on the surface or at periscope depth for the attack. That meant it was rarely deeper than about 63 feet.

Early in the war, captains were told to fire on sonar bearings. That wasn’t accurate enough and was discontinued. However, at that time the deepest firings were likely no deeper than 100 to 150 feet.

Ideally, when using the contact version of the exploder, the torpedo would hit the target deep enough to maximize flooding into the target but not so deep that the torpedo would inadvertently run under the target. The other consideration was the size of the ocean swells or waves. The torpedo sensed the differing depths due to large swells and sometimes porpoised as a result.

Once the approach officer identified the target and decided at what depth he wanted the torpedoes to run, he ordered that set into the torpedoes. This would typically be 15 to 20 feet for large ships and 7 to 10 feet for smaller targets. The depth setting was actually done in the torpedo rooms. The crew there used a crank to set the desired depth on a spindle.

Control of the depth after launching was originally done with a diaphragm and pendulum arrangement. After the depth problem with the Mark 14 torpedoes was confirmed, this was changed to an Uhlan gear, or planetary gear, system. This allowed the torpedo to recover more quickly and get to the desired depth. When the torpedo sensed that it was running too deep, the elevators at the rear of the torpedo would rise to point the torpedo at more of an up angle. (Torpedoes normally ran at a small up angle to compensate for its own weight.) Conversely, if the torpedo sensed it was too shallow, the elevators would lower so the weapon would run deeper.

The Gato/Balao/Tench boats usually carried 24 torpedoes. There were times when 24 torpedoes might not have been available. Manufacturing sometimes could not keep up with usage. That was solved after the Mark 18 electrics became available. The Mark 18s were easier to manufacture and there were a few more facilities were building them. However, it appears that the boats never went on patrol with fewer than 16 torpedoes.

The earliest fleet boats, those built in the 1930s, may have only carried 16. The later fleet boats generally were listed as carrying 24, although four of those may have been in external containers.

Visitors to museum submarines are often confused by the answer of 24. They don’t see where that many torpedoes can be stored. That is because 10 were stored in the torpedo tubes. In the forward torpedo room, there were six in the tubes and 10 reloads. Two of those reloads were below the deck plates. In the after room, there were four in the tubes and four reloads.

If there were still enough torpedoes on board, yes. The tubes would always be loaded at the beginning of a patrol. As torpedoes were fired, reloads would be moved into the tubes as soon as practical. Torpedoes would not normally be moved when under attack. The normal routine was first to escape. Then the submarine would be submerged so that there would be less motion from swells. That’s when they reloaded the tubes.

Because there was room for them. Submarines were travelling thousands of miles to their patrol areas and back. In order to make the trip truly worthwhile, the boats needed to take enough weapons. Instead of just 16 torpedoes in the forward torpedo room, now these latest boats could carry 24.

One reason would be that the target made a sudden course change (zigs or zags) and it became much easier to turn the boat to bring the after tubes to bear than to swing the bow that far around.

However, the captain also needs to remember to use those torpedoes sometimes, regardless of the situation. One-third of the available weapons were back there. Although it was probably a bit easier to plan the attack using the bow tubes, there was one distinct advantage to using the after tubes. As they were firing the torpedoes, they were already headed away from the target and beginning their escape.

One other factor could sometimes be subtle pressure from the crew. Using the torpedoes in the after tubes can improve the bunking situation. When the torpedo in the tube was fired, the reload was moved from the rack into the tube. In the after room, they could convert the empty torpedo rack or skid into bunks. Each skid could be converted into three bunks. When that was done, nine fewer sailors had to “hot bunk.”

There was no way to carry a torpedo through our WW2 boats from the after torpedo room to the forward room. In addition to the problem of the weight of the weapon, over 3,000 pounds, it was too long to make it through some of the bends in the main passageway. As a result, the torpedo would have had to be pulled up from the after room, moved over the side onto rafts and then pulled forward. It then needed to be hauled up on deck and moved down into the forward room. It was not a simple process and there was little mechanical help.

It seems that this was considered a few times but may never have actually been done on an American boat. One issue was that they would be exposed on the surface in a combat area for much too long a time. You would have had many men on deck and in the rafts. Large hatches would be open for quite a while. One captain was considering moving torpedoes when his mind was changed by a sighting of an enemy aircraft. Fortunately, this was before any work had been done to try to move a torpedo.

As mentioned, another big issue was the size and weight of the torpedoes. Another skipper began the process of moving a torpedo. However, he soon saw how much work was going to required and changed his mind. A third captain wanted to move some torpedoes from the after room to the forward room, but his weapons officer simply told him “No”.

Obviously, the best torpedo was the one that hit the target, exploded and sank the target. The advantages of the Mark 18 – the lack of bubble trails and the ease and speed of manufacture – would seem to make it a better torpedo. On the other hand, the Mark 14 had much higher speed leaving the target much less time to change course, either in a routine zigzag or when spotting the torpedo.The Mark 14 also had a larger warhead.

The problems with the Mark 14s and Mark 18s were generally resolved at about the same time.

The Mark 14 was in service much longer, until 1980. The Mark 18 was replaced in the mid-1950s.

As noted in the section “Attacks and Battles Small and Large”, that depends on a few things. What type of ship was it? Was it in good condition? What was it carrying? Was it fully loaded or nearly empty? What part of the target was hit? Here are some examples:

1. U. S. submarines sank only one Japanese battleship. The USS Sealion (SS-315) sank the battleship IJN Kongo in November of 1944. That required three hits from a salvo of six fired.
2. Carriers normally required multiple hits because of their size. However, the USS Albacore (SS-218) managed to sink the Japanese carrier IJN Taiho with a single torpedo hit. Albacore had help from a fatal mistake by Japanese damage control.
3. Sam Dealey, captain of the USS Harder (SS-257), was known as the destroyer killer. He sometimes used “down the throat” shots which meant the destroyer was coming directly at him to attack and he would charge at it. Dealey would fire torpedoes and the destroyer would try to turn away. That actually presented a wider target. Typically, only one torpedo would hit the destroyer but that would be enough. However, it was a very dangerous method unless it worked and few other captains used this method.
4. Hitting an ammunition ship usually resulted in a huge explosion and a quick sinking.
5. Hitting an escort ship near the stern might detonate their depth charges. That would likely sink the escort.
6. Gasoline tankers could explode with one torpedo hit. In that case, the explosion could be a blinding flash, and the ship would just be gone when the smoke cleared. However, if it were carrying crude oil, it might not sink unless a fire was started. (Crude doesn’t start burning easily but once burning is difficult to put out.)
7. An empty tanker could be very difficult to sink unless it was hit in the engineering spaces. Since the tanks were designed to be full of liquid, either oil or ballast water, a torpedo might only fill one tank with seawater. Such damage would need to be repaired but might have only slowed the ship a little.
8. The USS Salmon (SS-182) actually sank a ship with a torpedo that didn’t explode. It was an old ship and the dud torpedo punched right through its side. That was enough to flood and sink the target.
9. The Rakuyo Maru, the ship from which the Pampanito rescued the 73 British and Australian soldiers who were POWs, was carrying raw rubber. Although rubber was too dense to float, the fact that it filled that hold and absorbed most of the explosion, left the Rakuyo Maru sinking very slowly. It allowed the soldiers time to climb back aboard and to find a little food, water and materials for rafts before the ship finally sank.

Assuming that the torpedo was running on a straight course, it will just continue to do so. If they were lucky enough to fire at overlapping targets, the miss might hit the farther ship. Otherwise, when it ran out of fuel or electrical power, it just sank. It sometimes exploded when it hit the bottom, depending on the ocean depth and the makeup of the bottom.

Torpedoes were loaded through the torpedo loading hatch. At the USS Pampanito Museum, there is an example of the hatch on the pier, close to the beginning of the pier, up against the building. These hatches were cut out of the boat when the structures and stairs were installed for the museum entrances and exits. This was the strategy for nearly all WW2 museum submarines. The USS Cod (SS-224) Museum in Cleveland is an exception.

A torpedo was brought over to the submarine on a crane. It was balanced on a strap and it was lowered down to a short rack in front of the loading hatch. A safety cap was on the front of the torpedo with lines attached. The lines would be wrapped around a capstan, a spool shaped device. The capstan would be rotated until it took the weight of the weapon. Then the crane and strap would be released from the torpedo. The capstan would be rotated in the other direction to allow the torpedo to be lowered slowly through the hatch and into the boat.

Meanwhile, in the torpedo room, the empty skid was moved to the middle of the room to line up with the loading hatch. Then the end of the empty skid nearest the hatch would be raised up to meet the incoming weapon. This was accomplished using the chain falls, the pulley-like device that can be seen in the torpedo rooms. Once the torpedo had been loaded onto the skid, it was strapped into place, and the skid was lowered to level. Now the skid could be moved side-to-side to its final location. This only loads the torpedo into the boat. It may still need to be loaded into a tube.

This was a slow and careful process, as would be expected. Remember, the torpedo weighs 3,000 pounds or more and has at least 600 pounds of explosive at the front.

There is little documentation on this topic, but 20 to 30 minutes would seem to be a reasonable amount of time needed. That is considering the weight of the weapon, the route into the submarine and the hazards involved.

Sources vary but generally state that it was between five and ten minutes per tube. Some of the variation in the estimates might depend on how much of the work was done ahead of time, between the firing of the previous torpedo and the start of the reload.

Reloading was usually done while submerged so that the boat would be steadier. First, the outer door had to be closed and the tube drained. Then the inner door on the tube would be opened. The skid with the reload torpedo had to aligned with the tube. Ropes and pulleys were then used to haul the torpedo into the tube. Remember that the torpedo weighed as much as a small car does now. The skid had rollers to help move the torpedo along and the wooden blocks that cradled the torpedo were greased to reduce friction. Three men were probably enough to pull the torpedo into the tube, but there may have been additional men available to help.

The engine starting switch had to be up against the stop block so the engine would start as soon as the torpedo was fired. A spindle also had to be inserted from the tube into the torpedo so the gyro could be set from the TDC.

The torpedo explosive is called Torpex. It was also used in the depth charges that were used against the Axis submarines. Torpex consists of TNT enhanced with RDX and aluminum. RDX is an oxidizer which helps the explosive burn more efficiently. The aluminum provides more surface area for the explosive, again to help it burn more efficiently.

The Japanese torpedoes were probably the best. That was certainly true at the beginning of the war. The Germans may have been the most creative. The British torpedoes were very reliable. Our torpedoes were the worst, at least until the three most serious problems were fixed. That wasn’t accomplished until late 1943.

The Japanese torpedoes were clearly the most effective at the beginning of the war. The Type 93, now known as the Long Lance, was a famous torpedo that was actually a surface-fired weapon, from destroyers and cruisers. It was used most effectively in the various actions in The Slot or Iron Bottom Sound during the battles for the Solomon Islands (such as Guadalcanal). Their submarines fired the Type 95, which was very similar and just as effective. The submarine version had a warhead of almost 900 pounds. It used oxygen or hydrogen peroxide instead of air for combustion, and that gave them much greater range and less of a wake.

The single most effective spread of the war was fired by CDR Kinashi Takaichi in command of the IJN submarine I-19. Our intelligence did not believe that the damage he had wrought could have been done by one submarine. Only after the war, when JANAC compared records of all attacks and losses, did we realize that one spread had done all that damage.

CDR Kinashi had fired a spread of six Type 95 torpedoes at the carrier Wasp from about 1,000 yards. The Wasp was very vulnerable since she was refueling and rearming her aircraft. Three of the Type 95s with their large warheads set the Wasp ablaze and quickly sank it. Unknown to the Wasp or to CDR Kinashi, one of the misses continued about 12 miles until it ran into the battleship USS North Carolina. The damage put the battleship out of service for a few months until it could be repaired. Another miss found the destroyer USS O’Brien in that same area and damaged it badly. The O’Brien did not sink immediately. However, while she was being towed to San Francisco for repairs, she broke up and sank. All of this from a single salvo of torpedoes.

Another note about Japanese torpedoes. When any torpedo was fired it generally descended about 30 feet in depth until it got up to speed and came back up to the desired depth. Torpedoes dropped from aircraft run even deeper initially. During the attack on Pearl Harbor in 1941, this was an issue for their Type 91 airborne torpedoes. If they had descended that far in the harbor during the attacks, they would have been stuck in the mud. However, the Japanese designed breakaway fins on their torpedoes to keep them from going that deep.

German torpedoes were perhaps the most creative. They developed an electric version that we were eventually able to reverse engineer as our Mark 18. Germany also developed a torpedo that would run straight for a while and then started on a curved path. The idea was that if it hadn’t hit the immediate target, it would wander through a convoy hoping it would eventually find something else. They also developed a homing torpedo before anyone else for use against our escorts and cargo ships.

British torpedoes were not fancy, but they were reliable. They were diesel powered and ran straight and true. Curiously, when the British submarine HMS Conqueror sank the Argentine cruiser ARA General Belgrano during the Falklands War in the early ‘80s, the captain chose the WW2 Mark 8 torpedoes. The British were having problems with their brand-new Mark 24 Tigerfish torpedoes, and the skipper decided to go with the reliable Mark 8s. This was somewhat fitting since the General Belgrano was originally the WW2 American cruiser USS Phoenix.

A gyroscope is a set of spinning wheels or disks that tend to stay stable in space. The simplest examples are spinning tops or bicycle wheels. Once moving on a bicycle, it is easier to remain upright because the wheels are acting like gyroscopes and are stable in space. Torpedoes use gyrocompasses for the same reason. No matter which way the weapon turned, the gyroscope tended to stay stationary in space, pointing to the same direction. 

That did happen at times. Some of our older submarines that we had at the outbreak of the war, only had an internal capacity of 20. Some could, but didn’t always, carry four more in containers in the superstructure. That meant they would have to lower them into the torpedo room once space became available. Naturally, the boat had to be on the surface to do this work.

Early in the war, we were soon short of torpedoes. A large number were lost when they were destroyed by Japanese bombing in the Philippines. The steam torpedoes were complex to build, and the factories were not keeping up with the demand. As a result, some boats went out on patrol with 16 or 18 torpedoes.

The situation improved when we were able to reverse engineer a German electric torpedo. The electrics were easier, faster and cheaper to make. Westinghouse developed the electric Mark 18 torpedoes and built them. That gave us better production as well as increased capacity from additional plants. By late 1943,we were building enough electric torpedoes to begin to eliminate the shortage.

There were also times when submarines were carrying special supplies or other weapons in the tubes or on the torpedo skids, such as mines. At least two mines would fit in the place needed for one torpedo. These supplies and mines took up space that otherwise could have had torpedoes.

It most likely did. That would be based on the requirements for the TDC. A single spread or salvo of torpedoes probably needed to be of the same type. Otherwise, the TDC would need new information about the type of weapon being used in the middle of the firing sequence. The best situation would seem to be to load all of the same type torpedoes in each torpedo room. It could be different forward than aft and could still require the TDC to be reset, but it wouldn’t be in the middle of an attack.

Disastrous flooding. That was why there were interlocks that prevent both doors from being opened at the same time. The interlocks can be overridden, but that was normally only done in dry-dock, when flooding was not an issue.

Yes. In fact, one of the most important things to remember when torpedoes were fired was that the boat had suddenly gotten lighter. That mattered more when submerged because the sudden change in buoyancy can cause significant problems immediately. When firing torpedoes, the boat had suddenly gotten hundreds or thousands of pounds lighter. If they were firing six torpedoes from the forward tubes, the boat has discharged over 19,000 pounds. Some of that weight loss was made up from the water in the tubes that replaced the torpedo. The torpedomen might also be able to leave a drain valve open for bit to help compensate for the weight loss. In any case, the diving officers needed to be aware of the changes and may have needed to add weight in the trim tanks.  They certainly didn’t want to be light forward and broach.  They also don’t want to be light aft giving them a sudden down angle and an unplanned depth excursion.