# Armor-piercing shells 1. pass through soft targets 2. delayed detonation. With WWII technology? How? **URL:** \ **Category:** Factual Questions\ **Created:** [December 9, 2012, 2:50am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480 "2012-12-09T02:50:19Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 9, 2012, 2:50am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/1 "2012-12-09T02:50:19Z")
Few naval battles were as lop-sided as the Battle off Tamar in WWII. And fewer still are those where the lesser side of the ‘lop’ can claim to have emerged victorious. One of the reasons the US ships survived, or survived as long as they did during the engagement, was because the Japanese armor-piercing shells would often pass right through them without exploding. This occurred when the shells didn’t encounter sufficient armor at/after impact to detonate their fuses. So, paradoxically, the ships’ lack of armor _protected_ them. (As an aside, if the incoming shell managed to hit a reinforced structure such as a heavy support beam or the iron housing of, say, a propeller shaft, it would detonate; often deep within the ship) All that said, some of the Taffy III ships _did_ have at least 3/4" armor. And, even in the absence of armor, the ships’ hulls and much of the rest of their basic construction was of steel. So, my questions: _Especially with respect to technologies available at the time_: 1. how did the fuses work such that they would ‘ignore’ simple steel walls, bulkheads, and thin armor, yet be detonated by more substantial resistance? What mechanism enabled the fuses to ‘distinguish’ between the various hard sites they might strike? 2. generally (and again keeping in mind the ca. WWII technology) how did one get a delay on the order of milliseconds (in order to explode inside the target and not on its surface)? Thanks! ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 9, 2012, 3:21am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/2 "2012-12-09T03:21:24Z")
> [@KarlGauss](#): > > Few naval battles were as lop-sided as the Battle off Tamar in WWII. And fewer still are those where the lesser side of the ‘lop’ can claim to have emerged victorious. One of the reasons the US ships survived, or survived as long as they did during the engagement, was because the Japanese armor-piercing shells would often pass right through them without exploding. This occurred when the shells didn’t encounter sufficient armor at/after impact to detonate their fuses. So, paradoxically, the ships’ lack of armor _protected_ them. (As an aside, if the incoming shell managed to hit a reinforced structure such as a heavy support beam or the iron housing of, say, a propeller shaft, it would detonate; often deep within the ship) > > All that said, some of the Taffy III ships _did_ have at least 3/4" armor. And, even in the absence of armor, the ships’ hulls and much of the rest of their basic construction was of steel. > > So, my questions: > > _Especially with respect to technologies available at the time_: > > 1. how did the fuses work such that they would ‘ignore’ simple steel walls, bulkheads, and thin armor, yet be detonated by more substantial resistance? What mechanism enabled the fuses to ‘distinguish’ between the various hard sites they might strike? > 2. generally (and again keeping in mind the ca. WWII technology) how did one get a delay on the order of milliseconds (in order to explode inside the target and not on its surface)? > > Thanks! er, why are you treating “armor piercing” and “incendiary” as the same thing? ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [December 9, 2012, 3:23am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/3 "2012-12-09T03:23:34Z")
I am not entirely sure of the delay process. As to the armor piercing: the shells, themselves were “armored” in that their noses were built of heavier construction to allow them to penetrate other armor. The fuse was set back against the explosive and if there was not sufficient resistance that would crush the nose of the shell, the fuse would be untouched. (The weight of the nose was sufficient that an Armor Piercing 16" shell only carried 1,600 lbs. of explosives while a High Explosive 16" shell carried about 2,000 lbs. of explosive.) ETA: 3/4" of armor was really nothing to an AP shell from a heavy gun. They were designed to penetrate several inches of hardened steel. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 9, 2012, 3:25am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/4 "2012-12-09T03:25:01Z")
I missed where the OP said anything about incendiaries. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [December 9, 2012, 3:27am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/5 "2012-12-09T03:27:05Z")
> [@jz78817](#): > > er, why are you treating “armor piercing” and “incendiary” as the same thing? Where did he do that? ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [December 9, 2012, 3:45am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/6 "2012-12-09T03:45:46Z")
Regarding the 3/4" armor, [this link to a comparison of battleships](http://www.combinedfleet.com/b_armor.htm) across multiple navies shows armor on every ship selected thicker than 12". 3/4" armor was intended to stop 20mm cannon fire from strafing aircraft and splinters from nearby explosion, not actual cannon fire. Even tanks were carrying armor more than 2" thick by that point in the war. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 9, 2012, 4:16am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/7 "2012-12-09T04:16:34Z")
> [@tomndebb](#): > > As to the armor piercing: the shells, themselves were “armored” in that their noses were built of heavier construction to allow them to penetrate other armor. The fuse was set back against the explosive and if there was not sufficient resistance that would crush the nose of the shell, the fuse would be untouched. Excellent! Very neat - a low tech solution; simple, elegant, and reliable. Thanks. Clearly, 3/4" armor is negligible compared to what’s found on, say, a battleship. My intuition (which was clearly mistaken) was that even 3/4" steel would provide enough resistance to _detonate_ armor-piercing shells. But, with the mechanism you’ve described, it now seems intuitively to be the case that 3/4" could well be inadequate! ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 9, 2012, 4:19am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/8 "2012-12-09T04:19:25Z")
> [@jz78817](#): > > er, why are you treating “armor piercing” and “incendiary” as the same thing? er, what are you on about? Or, is that just an incendiary question? ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [December 9, 2012, 6:16am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/9 "2012-12-09T06:16:53Z")
An [article](http://www.navweaps.com/index_tech/tech-020.htm) on fuze construction that might be of interest. ---
**Author:** ![Dissonance](https://avatars.discourse-cdn.com/v4/letter/d/85f322/32.png) [@Dissonance](https://boards.straightdope.com/u/Dissonance)\ **Post date:** [December 9, 2012, 8:25am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/10 "2012-12-09T08:25:02Z")
> [@tomndebb](#): > > 3/4" armor was intended to stop 20mm cannon fire from strafing aircraft and splinters from nearby explosion, not actual cannon fire. Just to note 3/4" armor was the maximum belt armor on the destroyers, deck armor was 1/2" over machinery sections and 0" on the rest of the deck. To nitpick, the [Battle of Tassafaronga](http://en.wikipedia.org/wiki/Battle_of_Tassafaronga) can really give the Battle off of Samar a run for the money in terms of lop-sided odds and a lop-sided victory for the weaker force. A Tokyo Express run of 8 destroyers, 6 of them loaded with supply drums under the command of Tanaka bringing supplies down to Guadalcanal was intercepted at night by a USN force of 4 heavy and 1 light cruisers and 4 destroyers which took the Japanese by surprise. The Japanese reacted swiftly by having the column reverse course 180 degrees and launch torpedoes. Only one Japanese destroyer was lost, while the heavy cruiser _Northampton_ was sunk and all of the other 3 heavy cruisers were severely damaged; two of them having their bows blown off. The extent of the damage is clear in post action pictures of them; [USS Minneapolis](http://en.wikipedia.org/wiki/File:USS_Minneapolis_after_Tassafaronga.jpg), [USS New Orleans](http://en.wikipedia.org/wiki/File:NewOrleansTulagiBowMissing.jpg) and [USS Pensacola](http://en.wikipedia.org/wiki/File:USS_Pensacola_after_Tassafaronga.jpg). ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [December 9, 2012, 5:23pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/11 "2012-12-09T17:23:49Z")
Way more than you ever wanted to know about USN ammunition and fuzes: NAVSEA SW030-AA-MMO-010, [NAVY GUN AMMUNITION DESCRIPTION, OPERATION, AND MAINTENANCE](http://www.scribd.com/doc/55964981/NAVSEA-SW030-AA-MMO-010-TM-Navy-Gun-Ammunition-Usa-2004) (2004). The chapter on fuzes starts at page 80 of the 317 page document. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 9, 2012, 5:51pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/12 "2012-12-09T17:51:24Z")
> [@KarlGauss](#): > > er, what are you on about? Or, is that just an incendiary question? stems from my ignorance. so, nevermind what I’ve said previously in this thread. ---
**Author:** ![MOIDALIZE](https://avatars.discourse-cdn.com/v4/letter/m/e274bd/32.png) [@MOIDALIZE](https://boards.straightdope.com/u/MOIDALIZE)\ **Post date:** [December 9, 2012, 6:09pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/13 "2012-12-09T18:09:01Z")
> [@Dissonance](#): > > To nitpick, the [Battle of Tassafaronga](http://en.wikipedia.org/wiki/Battle_of_Tassafaronga) can really give the Battle off of Samar a run for the money in terms of lop-sided odds and a lop-sided victory for the weaker force. Tactically lopsided, yes. But in the end, they were prevented from completing their mission and delivering supplies to Guadalcanal. This battle also involved weapons that wouldn’t detonate. Unfortunately, they were American torpedos. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [December 9, 2012, 6:24pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/14 "2012-12-09T18:24:36Z")
To the OP IIRC it was deceleration which set the fuse of. A near 3000 ib shell fired at Mach 3 is not going to suffer much deceleration from hitting the thin skin of a destroyer, but it will suffer the a huge amount from the foot plus of armour on a battleship. The mechanism varied, some had a vial of acid which broke at a specific deceleration, others saw a pin released. Ideally you wanted the shell to explode when it had pierced the armour, causing general distress inside the ship, killing sailors, wrecking machinery, setting off British powder magazines etc. The biggest problem was actually getting the rounds to NOT explode until they had achieved the desired penetration. At Jutland, British rounds tended to detonate on impact against German ship, one of the reasons that the Germans were able to absorb such brutal amounts of punishments. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 9, 2012, 10:36pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/15 "2012-12-09T22:36:24Z")
> [@Gray\_Ghost](#): > > Way more than you ever wanted to know about USN ammunition and fuzes: NAVSEA SW030-AA-MMO-010, [NAVY GUN AMMUNITION DESCRIPTION, OPERATION, AND MAINTENANCE](http://www.scribd.com/doc/55964981/NAVSEA-SW030-AA-MMO-010-TM-Navy-Gun-Ammunition-Usa-2004) (2004). The chapter on fuzes starts at page 80 of the 317 page document. Thanks! But I was hoping for something a bit more detailed. 😉 I looked through the fuze section (actually, I looked through almost the entire document) and am starting to get a better sense of how the fuzes work, especially those of the pre-electronics era. In fact, your earlier link on “[How Shell Fuzes Work](http://api.viglink.com/api/click?format=go&key=ce270d38103a630c3181db372a25a052&loc=http%3A%2F%2Fboards.straightdope.com%2Fsdmb%2Fshowthread.php%3Fp%3D15778888%23post15778888&v=1&libid=1355092585555&out=http%3A%2F%2Fwww.navweaps.com%2Findex_tech%2Ftech-020.htm&ref=http%3A%2F%2Fboards.straightdope.com%2Fsdmb%2Fnewreply.php%3Fdo%3Dpostreply%26t%3D674955&title=Armor-piercing%20shells%201.%20pass%20through%20soft%20targets%202.%20delayed%20detonation.%20With%20WWII%20technology%3F%20How%3F%20-%20Straight%20Dope%20Message%20Board&txt=article&jsonp=vglnk_jsonp_13550926168712)” (post #9) also went over it (although I found the style of writing therein not quite what I might have expected :D). The bottom line seems to be that for shells of that era and type, there were delays on the order of milliseconds (6 to 13) which were set into action by (as **AK84** also points out) by the shell’s deceleration (or, phrased differently, by the continued forward movement of the firing pin which allowed it to plow into the primer which then, in turn, ignited a bit of black powder aft of the primer). What I am having a hard time believing is that millisecond precision could be achieved by the chemical process of burning black powder, especially when the entire apparatus had just experienced the monumental shock of being slammed into armor at some 2000 mph! At best, I would have expected something critical to have been jiggled loose by the impact thus making it a bit of a miracle that it still fired, and an absolutely huge miracle that the powder so ignited still burned for the precise number of milliseconds originally intended! (BTW, as a complete aside, the large Navy gun link above also helped resolve [a question I had asked here a few weeks ago about naval shells containing spotting dye](http://boards.straightdope.com/sdmb/showthread.php?t=673144). In fact, on page 3-29 of that document, figure 3-34 shows how the dye was placed. One sees there that the arrangement would have been unlikely to significantly alter the ballistics of the shell. See? I told you I looked through the entire document.) Thanks! I really do appreciate all the help everyone’s provided. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [December 9, 2012, 11:25pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/16 "2012-12-09T23:25:06Z")
> [@tomndebb](#): > > I am not entirely sure of the delay process. > > As to the armor piercing: the shells, themselves were “armored” in that their noses were built of heavier construction to allow them to penetrate other armor. The fuse was set back against the explosive and if there was not sufficient resistance that would crush the nose of the shell, the fuse would be untouched. > > (The weight of the nose was sufficient that an Armor Piercing 16" shell only carried 1,600 lbs. of explosives while a High Explosive 16" shell carried about 2,000 lbs. of explosive.) > > ETA: 3/4" of armor was really nothing to an AP shell from a heavy gun. They were designed to penetrate several inches of hardened steel. The 16" AP projectile has only 40.9 lb of explosive. (Explosive D, yellow D, etc.). This is out of a total weight of 2700 lb for the Mk 8 projectile. The Mk 13 and 14 HC (high capacity) shells weighed 1900 lb with an explosive weight of 153.6 lb. Pretty surprising how little an explosive charge. The delay comes from the design of the fuze and the fact that it’s installed in the base of the projectile. Most of what you need to know about US 16" guns and shells is at: > **[USA 16"/50 (40.6 cm) Mark 7 - NavWeaps](http://www.navweaps.com/Weapons/WNUS_16-50_mk7.php)** Note that this site has a picture that debunks any claim that a battleship broadside moves the ship sideways. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 9, 2012, 11:55pm UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/17 "2012-12-09T23:55:32Z")
> [@AK84](#): > > A near 3000 ib shell fired at Mach 3 is not going to suffer much deceleration from hitting the thin skin of a destroyer . . . I understand and don’t disagree. Still, in one of the pages at **smithsb** ’s link above, the statement is made that for the US Navy at least, the fuse of armor piercing shells would activate so long as the shell encountered (at 0 degrees obliquity) [just one inch of armor plating](http://www.navweaps.com/Weapons/Gun_Data_p2.htm) (cited part is about 15% deep in the linked page, under section entitled, “Fuzes”). ---
**Author:** ![TonySinclair](https://avatars.discourse-cdn.com/v4/letter/t/49beb7/32.png) [@TonySinclair](https://boards.straightdope.com/u/TonySinclair)\ **Post date:** [December 10, 2012, 12:36am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/18 "2012-12-10T00:36:14Z")
> [@tomndebb](#): > > > [@](#): > > > > Originally Posted by jz78817 > > er, why are you treating “armor piercing” and “incendiary” as the same thing? > > Where did he do that? I think jz might be making a snarky distinction between “fuse” and “fuze.” ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 10, 2012, 2:39am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/19 "2012-12-10T02:39:33Z")
> [@TonySinclair](#): > > I think jz might be making a snarky distinction between “fuse” and “fuze.” Very snarky if so. I thought the difference was strictly a British English versus US English thing. Like armor-piercing and armour-piercing 😉 ---
**Author:** ![Aji\_de\_Gallina](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aji_de_gallina/32/260_2.png) [@Aji\_de\_Gallina](https://boards.straightdope.com/u/Aji_de_Gallina)\ **Post date:** [December 10, 2012, 3:04am UTC](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480/20 "2012-12-10T03:04:22Z")
Durin the Falklands War, many bombs fro Argentinian A-4s would pass through ships without going off because the fuse hadn’t been activated due to the short time the werr “flying”. I can guess a similar thing happened. [Next page](https://boards.straightdope.com/t/armor-piercing-shells-1-pass-through-soft-targets-2-delayed-detonation-with-wwii-technology-how/643480.md?page=2)