What torpedoes did our submarines use during WW2?
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 It had been superseded by the Mark 14 by the beginning of the war, but there was still a limited supply available.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.)