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I'm listening to James Scott's "The War Below". In World War II, US Navy torpedoes detonated at the end of their range if they hadn't hit anything. So if a torpedo was fired and went its maximum range (4500y for the Mark 14) without otherwise detonating, it would self-detonate.

I'm curious why that is advantageous? Wouldn't it make more sense for a missed shot to be allowed to silently sink to the bottom? I'd think there would be many tactical situations where a commander would prefer that if his shots missed, the enemy remained unaware until he could shoot again.

There are numerous scenes in the book where commanders hear detonations that are long after the calculations showed they should have exploded if they'd hit, etc. so it was apparently standard.

To be clear, I'm not talking about any of the malfunctions or problems the US Navy had with its torpedoes in WWII. The torpedoes of that era were designed to explode at end of run.

A few related questions:

(1) Was that true only of the US Navy or did the torpedoes of the Germans, Japanese, etc. behave the same way?

(2) When the USN switched from steam-powered to electric-powered torpedoes, was this design carried forward?

(3) Do torpedoes still behave that way? I realize nowadays they seek their own targets in some cases but what if a torpedo is fired and runs out of power...self-detonate or sink to the bottom?

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    Are you asking about before or after Admiral Lockwood took on the Bureau of Ordanance so that they'd work at all?
    – KorvinStarmast
    Commented Feb 25, 2017 at 2:36
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    At a guess, this was so they wouldn't cause problems later as unexploded ordinance.
    – user15620
    Commented Feb 25, 2017 at 3:43
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    Supposing the torpedo does not sink, or ends its run in shallow water. It then poses a danger to any ship which bumps into it.
    – jamesqf
    Commented Feb 25, 2017 at 4:39
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    I guess it also can be an advantage that they don't fall into enemy hands.
    – liftarn
    Commented Feb 27, 2017 at 8:54
  • @liftarn early US torpedoes would make Japanese navy people die of laughter if they saw them :)
    – jwenting
    Commented Sep 22, 2021 at 7:07

4 Answers 4

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To prevent torpedoes from becoming a navigational hazard in the event of a miss the 1907 Hague Convention VIII had a section on mines.

Once a torpedo was out of fuel it was buoyant. Therefore any torpedo that missed its mark (which was a lot!) would become a random and deadly hazard to navigation. The easiest solution to this was to detonate the torps at the end of run when the fuel ran out.

In later models, they were built to automatically explode when the fuel was exhausted. US submarine commanders speak of hearing 'end-or-run' explosions which told them their torpedo had missed.

This may be designed as safety system, causing the torpedo to self-detonate after a certain radius.

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The reason is simple: nobody wants an uncontrolled explosive device floating around. You yourself, or someone else, other then your enemy may later accidentally hit it. For the same reasons all anti-aircraft shells explode at the end of their trajectory: who knows what they may hit on the ground.

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  • so true, that pieces of antiaircraft shells falling on the ground were a major reason to keep people indoors or in shelters during WWII bombardment. Imagine if the shells were still live! All that goes up, goes down!
    – Luiz
    Commented May 28, 2018 at 17:45
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    @Luiz: The main reason for people to stay indoors, in cellars or bunkers, during bombardment were the bombs of the bombardment...
    – DevSolar
    Commented May 29, 2018 at 8:13
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    I really wrote something strange. True. But a lot of flak may appear even if the bombs are not falling "here and now". Even when planes are just passing or returning. So even if all enemy planes are going in their home direction, they are still dangerous because of friendly flak. This is what I meant.
    – Luiz
    Commented May 30, 2018 at 19:13
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    @DevSolar : not only that. During WW2 there was a false alarm in Los Angeles, where anti-aircraft batteries started firing at an enemy which wasn't even there. The result: several buildings damaged by falling shrapnel, five civilians dead. Imagine how much more damage would have been done, if the shells didn't explode high in the air, and instead of fragments falling down from the sky there would be intact shells falling and then exploding.
    – vsz
    Commented Apr 15, 2020 at 5:01
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Kriegsmarine had two torpedoignitors with relevant devices:

  • Pistole 4c EDS (Pi4c EDS)
  • Pistole 4d SZE (Pi4d SZE)

EDS = Endstreckendetonierersicherung ("safety against end-of-run-detonation") SZE = Selbstzerstörungseinrichtung ("selfdestruction-device")

The Pi4c EDS was only used in Type Ke and Type Ke1 warheads with the passive acoustic seeeking G7e(TV) "Zaunkönig" and G7e(TXI) "Zaunkönig II" torpedoes (only used from submarines).

The Pi4d SZE was only used in Type Ke and Type Ke1 warheads with the G7e(TVa) torpedo - a specially adapted variant of the "Zaunkönig" for S-Boote (ie MTB's).

EDS would permit detonation of the warhead of a torpedo hitting the seabed after missing the target, to avoid giving away the presence of a submarine in the area. SZE was primary a device incorporated to prevent new and advanced technology falling into enemy hands (the S-boote operated close to coastlines in shallow waters with much higher risk of missing torpedoes ending up running ashore etc).

Sources: Various Kriegsmarine handbooks, including "Technische Dienstvorschrift Nr. 194 Torpedo-Kopf-Pistolen-Tabelle" (Kriegsmarine, 1944) and "Torpedo Zünder der Deutschen Marine von 1914 bis 1968 mit historischen Rückblick, Band 1" (Bundesmarine, ca 1970).

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    @MCW quote from OP, emphasis mine: "(1) Was that true only of the US Navy or did the torpedoes of the Germans, Japanese, etc. behave the same way?"
    – Jan
    Commented Sep 22, 2021 at 5:35
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another reason beside safety issues: suppose a torpedo misses. Then it keeps floating, sinks in shallow water, or reaches land and is beached. If it does not go BOOM the enemy might recover it!

Even if there are no tech secrets, the enemy might learn about the state of your industry by checking the quality of components and assembly. Or deduce something about your logistics chain or unit positions by examining part numbers or markings.

It is interesting e.g., how the allies deduced the number of Panther tanks produced by analyzing sequential part numbers. Or how today South Koreans analyse the wreckage of North Korean missiles and subs.

Deny information to the enemy: if it is ours, and the enemy might get it, them GO BOOM! It will make harder for them to deduce information (albeit not impossible, as in the Korean example above)

For the same reason, if a damaged plane was forced to land where the enemy could get it, friendly planes would attack it (after making sure the pilot was not there)

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    This sounds plausible to me except for the last paragraph (which I have serious doubts about based on a reasonable knowledge of air attacks in Germany during WW2). Adding some references would improve this answer.
    – njuffa
    Commented May 29, 2018 at 5:16
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    @njuffa: For example ref. the Akutan Zero. This was, of course, situational.
    – DevSolar
    Commented May 29, 2018 at 8:19
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    @DevSolar: That is a useful link which would make a great addition to the answer. It offers confirmation for the first four paragraphs, which are not seriously in doubt. I still find the last paragraph pretty implausible.
    – njuffa
    Commented May 29, 2018 at 9:26
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    @njuffa: "Koga's wingmen, circling above, had orders to destroy any Zeros that crash-landed in enemy territory, but as they did not know if Koga was still alive, they could not bring themselves to strafe his plane."
    – DevSolar
    Commented May 29, 2018 at 9:54
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    good link. It is obviously a situational issue. It supposes the friendlies can locate the crash site, can see that it is more or less intact and not just a fireball, can see that the pilot is not there, and still find time to do it after a battle! Not easy or often done! I believe that orders like these japanese had about the Akutan Zero are common - but not expected to be fulfilled often.
    – Luiz
    Commented May 30, 2018 at 19:41

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