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"Circular Error Probability" of WWII bombs?

Discussion in 'Air War in Western Europe 1939 - 1945' started by Wild Turkey, Nov 2, 2014.

  1. Takao

    Takao Ace

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    Sufficient AA ammunition could be very subjective. More so, since most of the main battery guns of the RN and IJN lacked sufficient elevation to engage high flying targets. IIRC, with most RN destroyer guns being limited to +30 or +40 degrees and carrying mostly SAP ammunition instead of HE(ammunition was, for the Tribals, 200 SAP, 50 HE, and 50 ILLUM rounds per gun). The same is said of the early IJN destroyers, as the were mostly limited to +40 or +55 degrees elevation, but carried about 120-150 rounds per gun.
    http://www.navweaps.com/Weapons/WNBR_47-45_mk9.htm
    http://www.navweaps.com/Weapons/WNJAP_5-50_3ns.htm
     
  2. phylo_roadking

    phylo_roadking Member

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    Indeed; usually, when it comes under discussion....during the Crete evcauation, or off Norway...it's usually discussed in terms of how many attacks can be held off across what period of time when transiting into/out of airspace dominated by the enemy.

    "Sufficient" therefore isn't a count of rounds...it's whether you've enough to keep t'buggers off while you steam at full speed to get out of range - or whether you don't...

    It's a yes/no rather than "what have we got in the racks?"...as "no" tended to be very fatal.
     
  3. bronk7

    bronk7 Well-Known Member

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    optimally, carriers would be moving close to 30 knots, zigzagging, turning to avoid Divers
     
  4. phylo_roadking

    phylo_roadking Member

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    The problem with that, and steaming at full speed into the wind when launching/recovering aircraft, was that aircraft carriers' engines tended to wear out very quickly, and they required very regular recommissioning.

    During the Interwar period, The RN's carriers were ALWAYS one being recomissioned and at least one or more requiring it...and on the eve of war and into the first couple of years of wartime operations were no different. in fact possibly worse as the RN's money had in the two years immediately preceeding the war gone into new classes of destroyers and a couple of new light cruisers IIRC. Which is why you often see comments on the carriers' conditions and performance in various campaigns.
     
  5. harolds

    harolds Member

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    Back again to the AA on destroyers if I may: What Takao and P_R are telling us is that most destroyers in the early war years had to rely on light AA to fend off air attack. Was the USN the exception here with the 5"/38? I assume that the RN relied on the 1" pom pom, the USN on the 40mm Bofors and 20mm Orlikons and the Japanese on the 23mm(?). Correct?
     
  6. Takao

    Takao Ace

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    Early in the war, for the US, it was the 1.1 inch quad(the 40mm Bofors would supersede it in late '42 - early '43) and the 20mm Oerlikon(with the .50 caliber for the very early months)

    For British destroyers, there usually was one 3-inch/12-pounder as a "heavy" AA gun, with a sprinkling of 2-pounder, 20mm Oerlikon, and quad .5-inch MGs.

    The early Japanese destroyers really had only the 23mm and a smattering of 13mm MGs for AA defense. Later classes had their 5-inch gun elevation increased to 75 degrees, however, they lacked power ramming and had to be lowered back down to between 5 & 10 degrees for the gun to be reloaded.
     
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  7. phylo_roadking

    phylo_roadking Member

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    IIRC only a couple of classes of destroyer were equiped with this in the first years of the war, usually aft of the superstructure.

    The 2-pdr pompom was never regarded as a total success, despite it being in almost every newsreel of war at sea you see! It didn't turn out to have a great altitude/range. But at least they had it...

    Part of the problem was that noone really excpected to have to stand off really concentrated air attack by land-based aircraft ;) An occasional raid by carrier-based planes out in deep blue water, yes...but the Italian bombardment of Spanish shipping during the SCW was very late in the day for designers to learn...and then the first years of the war shaped up very differently than anyone expected. No real concentrated...or effective...RN blockade of Nazi Germany out at sea;

    Instead, repeated operations under the land umbrella....off the coast of Norway, off the French coast in late May/early June 1940, then the Channel convoys, then Crete, Tobruk, Malta....

    It was a hard and painful series of lessons for the RN year after year.
     
  8. lwd

    lwd Ace

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    That was IJN doctrine from what I've read. US doctrine was that the carrier formation would move as a unit at least until the very last moment. This made wild evasive maneuvers rather difficult but increased the accuracy of the AA fire, especially the formation AA fire enough that the USN thought it worthwhile. The fact that aircraft carriers had a fair amount of inertia and there was usually a fair number of dive bombers diving sequentially would also tend to make avoiding all of them difficult. Of course at Midway the IJN didn't see the dive bomber that hit the first 3 until they were pitching over.
     
  9. lwd

    lwd Ace

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    To supplement this here's the page on the US 5"/38.
    http://www.navweaps.com/Weapons/WNUS_5-38_mk12.htm
    Note that you can find the info on most naval AA weapons of the war by drilling down through the links at:
    http://www.navweaps.com/Weapons/index_weapons.htm
    Here's a good page on IJN AA
    http://www.combinedfleet.com/guns.htm

    My understanding is that one of the problems off Crete is that it wasn't realised at some points in the command chain just how important AA ammo supply was and that several of the ships lost were ordered back into range of German and Italian aircraft with low AA ammo supplies. The impression I got from somewhere is that at least the details weren't relayed to the Admiral in charge at the time
     
  10. mcoffee

    mcoffee Son-of-a-Gun(ner)

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    I'm wondering where this comes from. Boilers and steam turbines are not exactly 'wear' items.
     
  11. lwd

    lwd Ace

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    With a 1000 lb bomb most of the damage will be due to the filler. However you need enough velocity to penetrate the target to get the most out of it. The KE of the bomb is .5 * mass * velocity * velocity, so if you double the velocity you get 4 times the KE. According to http://en.wikipedia.org/wiki/TNT_equivalent
    A ton of TNT is aproximately 4000 mega jouls Looking at the IJN type 2 No. 50 bomb at http://en.wikipedia.org/wiki/List_of_Japanese_World_War_II_navy_bombs
    It weights in at 1,100 lbs or aproximately 550 kg and carries 148 lbs of explosive so ~300 mega joules of energy from explosives. The speed of sound is ~340 m/s so if we compare the same bomb at 300 m/s and 400 m/s the KE is 225 vs 400 mega jouls. However some of that energy is lost penetrating the structure and some may be lost due to over penetration. In the case of a naval vessel however over penetration may actually do more dame if the detonation is under the vessel. I also may have screwed up my math above so PLS check it. I was rather surprised to see the KE was that close to the chemical energy. From the fuzing I suspect that above bomb is a SAP although comparing it to other bombs it looks to me like it may be an AP bomb as it only has ~15% of its weight as HE where other bombs on the list run in the 30% to 50% range. Note that this means that



    There's a decent description of them in the last paragraph at:
    http://www.constable.ca/caah/bombs.htm
    They were designed to essentiall cause damage by cavitation be it in earth or in water. Certainly it would have more KE going faster but the damage cause to the intended target would likely vary by penetration depth. The ones that hit Tirpitz probably doing more damage because they penetrated and detonated under her. If they had pentrated to any depth in the ground under neath her I don't know what the effect would have been. The ground might have absorbed some of the energy from the blast or it may have focused it.

    Incidently for KE vs chemical energy effects in much smaller projectiles there's a good discussion at:
    http://www.quarry.nildram.co.uk/
    but I can't get to it right now. You have to follow a couple of lengths to get to the mg vs cannon / fighter armament discussions.
     
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  12. phylo_roadking

    phylo_roadking Member

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    Hurr Hurr, that was Ermie Cunningham's story - and he stuck hard to it! Even as far as dashing off his wartime memoir about three and a half minutes after the end of the war :) His conduct of various points in the Med campaign had already come under criticism and he wanted HIS version in print first. It's the RN's version of the debate over Freyberg's decision making on Crete, or the RAF's "Big Wing Controversy".
     
  13. lwd

    lwd Ace

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    I do suspect that there was a general lack of recognition about how critial the ammo supply was. How far up the chain the information went and what it conveyed is an interesting and IMO open question. I'd love to hear more if you have any recomendations.
     
  14. phylo_roadking

    phylo_roadking Member

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    I'll try and find out the name of Cunningham's book. I do know that "Crete 1941: The Naval Battle"....previously published in the 1950s under another title, just like Fleming's book on Sealion....was another party's reply in effect to Cunningham ;) I've got it buried somewhere, I'll try and find it and post up the details.
     
  15. Carronade

    Carronade Ace

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    Cunningham's own book was called A Sailor's Odyssey.
     
  16. bronk7

    bronk7 Well-Known Member

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    ....any experts out there can tell me dive time of bombers attacking ships from start of dive to bomb drop point??
     
  17. bronk7

    bronk7 Well-Known Member

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    much thanks..again, very enjoyable and informing on the details....maybe Takao can shout here<>later in the war, the Japanese DBomb pilots weren't as good as the original cadre?? so, AA fire was a better option than maneuvering?? [more AA ships also ] what about early in the war, about US carrier doctrine<>there weren't as many carriers and AA ships...was it still doctrine to maneuver as a unit or singly??
     
  18. lwd

    lwd Ace

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    Even early in the war it may have been a better option if you had sufficient AA on the carrier plus escorts. Remember the purpose of the AA is to protect the friendly targets not to shoot down enemy planes. While the latter is the preferred method heavy AA fire can "disrupt" the aim and lower hit probabilities substantially.

    A couple more sources you may want to consider.
    The First Team and Shattered Sword
     
  19. Carronade

    Carronade Ace

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    In the 1942 battles, US carriers operated individually, each surrounded by a ring of up to ten escorts. Two-carrier groups like TF16 at Midway comprised two of these formations operating a few miles apart, out of each other's way (and gun range) but close enough to observe each other's operations and communicate by visual signal or TBS radio. Each carrier - presumably the enemy's main target - was free to maneuver, and the rest of its formation conformed to its movements - or stayed out of the way ;) As I understand it, the carrier would still usually hold a steady course as long as possible to get the maximum effect of AA fire, where the Japanese would start weaving and circling as American aircraft approached.

    By 1943 we had enough carriers that they had to operate in task groups of 3-5, several of which would form a task force. This made it more dangerous for the carriers to maneuver, especially if more than one appeared to be under attack. Also by then our AA gunnery was more powerful and efficient, plus fewer of the enemy were getting through our CAP to be engaged by guns. So holding course became the primary tactic .
     
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  20. lwd

    lwd Ace

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    I haven't seen any official word on it but my impression is that they also tried to make sure at least one of those escorts was an Atlanta class CL.

    Verry good summary Carronade, more informative and better worded than mine.
     

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