What were the issues with the Japanese torpedoes?
At least one senior Japanese officer complained at the end of the war about the submarines and weapons they produced. However, it is not clear whether he was just shifting the blame or there were more problems with their boats. It could well be the former – blaming someone not in the operational chain of command. (His comments are found in “Sunk; The Story of the Japanese Submarine Fleet 1941-1945” by Mochitsura Hashimoto, page 244.) A conclusion by S. Fukutome, Former Chief of Staff of the Combined Fleet:
“What were the reasons for these deplorable results? They were largely due to our inferiority in the fields of ordnance and ship construction. Our submarines, built and equipped with inferior weapons, were counterattacked by the enemy before they ever got to their targets, or were evaded. Against the superior equipment of the enemy submarines our ships under attack had no opportunity to counterattack or evade. Many of them were alive [sic] to the enemy’s presence only after they were attacked.”
Whether his comments are legitimate or not, Japanese torpedoes at the beginning of the war were still the best by far even with a few issues. Although most of these problems were related to the torpedoes fired by surface ships, the submarine Type 89 and then the Type 95 submarine torpedoes were very similar.
The first issue is related to the fact that the Japanese used pure oxygen in their torpedoes rather than air for combustion. This was a great feature for these torpedoes because it gave them a much greater range and left virtually no bubble trail. Oxygen is about 21% of normal air. Therefore, pure oxygen would last about five times as long as the same amount of air. Most of the products of combustion with pure oxygen were water and a small amount of CO2 that would largely be absorbed by the sea.
The Japanese worked on oxygen torpedoes from 1920 until 1935 before the weapon was satisfactory. During the development of these torpedoes, the Japanese experienced explosions when the engines first started. This was solved by using another, smaller flask of normal air when the torpedo was first fired. The air flask was used first. As that flask was used, the air was replaced by the pure oxygen in a second larger tank. By the time these torpedoes reached the fleet, this problem had been solved. However, handling pure oxygen is always a hazard.
Because of the dangers in handling pure oxygen, torpedomen were described as the most highly skilled of the crew. The rest of the crew were told that the second (pure oxygen) tank was just another air flask. The Japanese installed bulky oxygen-producing equipment in both cruisers and destroyers but not in submarines. If a submarine’s Type 95 torpedoes needed to have the oxygen topped off, the boat would have to go alongside a cruiser or destroyer.
NOTE: It is hard to imagine that such information could be kept from the rest of the crew in the close confines of a submarine. However, Japanese culture was more structured and more formal than others and that may well have been the policy. Still, there would be so many clues that the rest of the crew could not help but see.
NOTE: Some sources refer to these torpedoes as “oxygen-fueled.” That is not technically accurate. The fuel in the Japanese torpedoes was kerosene. Pure oxygen was used rather than normal air as the oxidizer to burn the kerosene fuel.
The second issue was that the explosive in their warheads appeared to be very sensitive. (Warheads were filled with Shimose, a mixture of 60% TNT and 40% hexanitrodiphenylamine or HND, a booster class explosive.)
One possible factor in the sensitivity of the Type 93 warheads might be the setting by the crews. “Many accounts of the 1942 battles describe these torpedoes prematurely detonating after running the arming distance or detonating once they crossed the target’s wake. For example, it was estimated that about a third of the torpedoes launched at the Battle of the Java Sea (Sea Engagement off Surabaya) either prematured or detonated on wakes. An investigation by CDR Takedai Takashi of the Navy Technical Department, who was in charge of torpedoes at that time, found that approximately half of the torpedo fuzes returned for examination from warships involved in this battle would activate at pressures much lower than those specified. However, torpedo fuzes examined at the naval arsenals and at military supply departments worked properly. Further investigation found that the main cause for the self-destruction was that the torpedo crews on the ships were resetting the fuzes to a lower level in a misguided effort to ensure detonation. Post-war, Rear Admiral of Engineering Oyagi Shizuo, an authority on the Type 93 torpedoes … remarked in his recollections: ‘It was a matter of eternal regret that we had provided each vessel with a sensitivity adjuster for the fuzes.’”
(http://www.navweaps.com/Weapons/WTJAP_WWII.php" rel="noopener noreferrer" target="_blank">http://www.navweaps.com/Weapons/WTJAP_WWII.php; http://www.navweaps.com/Weapons/WTJAP_WWII.php" rel="noopener noreferrer" target="_blank">, section for Type 93 torpedoes.)
There were a couple incidents when Japanese cruisers experienced the sensitivity of their Type 93 torpedo warheads. Perhaps the best example of the issue is the outcomes for the cruisers IJN Mogami and IJN Mikuma in the later stages of the Battle of Midway. The two cruisers, along with others, had been sent to shell Midway after the carrier battle had already been decided. They were then recalled before they reached Midway. However, during the maneuvering to change course and return to the fleet, the two cruisers collided. Mogami then jettisoned her Type 93s, whereas Mikuma did not. As they were limping home, our aircraft found them and attacked. Mogami appeared to absorb more blows than the Mikuma but survived. Mikuma sank during the fighting when her own torpedoes detonated while still onboard. Mogami made it home for major repairs but was lost a couple years later when she was sunk during the Battle of Leyte Gulf.
Another example of the danger was thought to be the heavy cruiser IJN Chokai during the battle off Samar in October of 1944. In that case, a desperately lucky 5-inch shot from the fleeing escort carrier USS White Plains (CVE-66) reportedly hit the Chokai in the torpedo tubes. The resulting explosion then severely damaged the cruiser, and she had to be scuttled. However, another source disagrees with the identity of a cruiser sunk by her own torpedoes during that battle. “[T]he 2019 discovery by the RV Petrel of the wreck of the Chokai with her torpedoes intact disproved this theory. The same Samar engagement saw the heavy cruiser IJN Suzaya sunk by the detonation of her Type 93 torpedoes: a bomb near miss starboard amidships set off the torpedoes in the starboard tube mounts; the resultant fires propagated to other torpedoes nearby and beyond; the subsequent explosions damaged one of the boilers and the starboard engine rooms and eventually reached the main magazines.” It appears that at least one Japanese cruiser in this battle was sunk by her own exploding torpedoes although it is not clear which.
https://en.wikipedia.org/wiki/Type93torpedo" rel="noopener noreferrer" target="_blank" style="background-color: white; color: black;">https://en.wikipedia.org/wiki/Type93torpedo