Did RN Illustrious Class armoured decks provide significant benefit against bombs?

Discussion in 'Aviation' started by freebird, Dec 2, 2010.

  1. freebird

    freebird Active Member

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    Would the Illustrious have survived the Jan - Mar 1941 attacks without the armoured deck?
    Were the bomb hits on Indomitable Formidable survivable because of the armoured decks?
     
  2. davebender

    davebender Well-Known Member

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    Armored ship decks only protect against relatively small bombs, rockets and machinegun fire. Once the bad guys start using 1,000kg bombs (Ju-87D) and Fritz X guided air to surface weapons (Do-217 and He-177) then it's impossible to add enough deck armor.
     
  3. parsifal

    parsifal Well-Known Member

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    I disagree. The armoured box (calling it an armoured deck is misleading) has the effect of containing the blast, and limiting the damage. Removing or reducing the armouring on a ship means even small bombs do a lot of damage. This was why the Allied Navies were loathe to commit some of their cariers to hazardous operations, or when they did, they suffereed heavy losses for it. Though all British carriers that were lost, with the exception of the Herpes, were all lost because of weaknesses or failures in their protection systems, of which the armouring was a part.

    Now, having said all that,what is true is that armouring was found to be expensive and not cost effective. Moreover the penalties paid by the british in armouring the Illustrious class to the extent they did, was to reduce their aircraft complements. though this was the right decision for the RN at the time ....they simply lacked the aircraft to put big CAGs to sea, this was ultimately less effective than the big USN carriers.....aircraft are the best defences, not armour plate. The British also found they could emulate the armoured box principal less the armour, in their Collossus and Majestic classes. these adopted the closed box principal developed in the Illustrious class, but did not armour the deck. Tests postwar showed this arrangement to be very strong and resistant to bomb damage at low cost in weight. There were good reasons why the minor navies post war wanted these carriers over the ex USN CVLs...they were judged to be far more survivable....

    The British did realize this and eventually built large numbers of relatively simple hull structure and no armour scheme. they realized that a variation to the USN schemes was to have a large number of aircraft, but also to have a large number of hulls. this would have given them greater flexibility and would not have crippled their fleet if one of the bigger carriers were lost.

    They also realized that speed was not as important as the weight penalties, costs and complexity required. the differences in thes terms to building a 27 knot ship and a 33 knot ship simply could not be justified. Whereas in a Battleship action 3 or 4 knots difference in speed might make all the difference, such difference in carriers, whilst nice to have, was also not crucial. A ship pulling away, or closing at 4 knots per hour, is going to be sunk long before it gets into action, provided there are enough planes being carried to sink the faster ship.

    So, in conclusion, in the context of what the british were labouring under, ie a very small FAA, armouring the ships was absolutely the right decision, and very much improved their survivability. However it was not an optimum strategy. The optimum strategy would have been to have a much larger FAA overall, and then build a larger number of Colossus or Majastic classes to take them to sea. But given the 150 carrier planes that they had at their disposal (roughly speaking), and the growth rate of 16 pilots per year they were getting in 1938, when the Illustrious was designed. this was absolutely the right thing to do.
     
  4. parsifal

    parsifal Well-Known Member

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    After all, look at the way Illustrious survived numerous bombs in January 1941 in the Mediterranean and Formidable survived two 500 kg bombs in the Med on 26 May 1941 and even a couple of kamikazes off Okinawa in early May 1945, all with minimal casualties. On the other hand, Essex class carriers, such as Franklin (CV-13) reported 989 casualties and severe damage on 19 March 1945 from two 250 kg bombs while Bunker Hill (CV-17) had 650 casualties and equally severe damage from two kamikaze hits on 11 May 1945.

    To be fair, this sort of comparison is somewhat biased. Authors, such as Stuart Slade and Richard Worth, point to a host of critically important variables that must be taken into account before coming to a reasoned conclusion. They make a good argument that the different damage reported by British and American carriers were explained as as much by the amount of refuelled and rearmed aircraft on deck when the bomb or kamikaze hit than can be attributed to the different armouring schemes. Put simply: the bigger and more volatile the deck park, British, American or Japanese, the heavier the damage, regardless of whether the flight deck was armoured or not. One corollary found proven was that if a bomb penetrated the British flight deck armour, the damage was likely to be long-lasting and severe. Another was that good damage control procedures were vitally important. A third potentially confounding factor, frequently overlooked in comment, is that there were only four British fleet carriers exposed to kamikazes and they were rarely subjected to the heavy sustained attacks experienced by American carriers. Except to prove an exception, even the dodgiest statistician could never rely on such a small number as four.
     
  5. freebird

    freebird Active Member

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    This was from another website
    (illustrious 1941)


    1. A 500 pound bomb hitting directly on S2 pom-pom.
    2. A 1000 pound bomb passing through the port forward end of her flight deck, exploding 10 feet above water inside the ship.
    3. A 1000 pound bomb passing through her (unarmored) after lift and exploding 10-20 feet below the lift platform.
    4. A 1000 pound bomb passing through the armor deck on the centerline, which exploded above the after hangar and started a serious fire in the hangar.
    5. A 500 pound bomb hit on the after lift well.
    6. A 1000 pound bomb passed through the P1 pom-pom and failed to detonate.
    7. A 1000 pound bomb near-missed the aft starboard side.
    8. A 500 pound bomb which hit her in Malta, passing through the after lift.

    The armoured deck did nothing to prevent the bomb damage; the 1000-pound weapons (well above the rated resistance of the deck in any case) passed cleanly through and wrecked a lift and a hangar. A Yorktown would likely have not sunk from these hits either, as none of them did below-waterline damage.


    Would the amoured deck have retarded the impact velocity of the bomb enough to make a difference in when it blew?
    Were the bombs "fused" the same way that shells were, and could the deck have helped "decapping'?
     
  6. renrich

    renrich Active Member

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    I have read that the armored flight deck British carriers that were heavily damaged in WW2 were found to be not worth repairing after the war because the heavy structure necessary for the flight deck was so deformed by the bomb damage. Is that accurate?
     
  7. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Yep, HMS Herpes :shock:

    (sorry, just could not resist it)
     
  8. Nikademus

    Nikademus Member

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    Kilograms....not Pounds.
     
  9. timshatz

    timshatz Active Member

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    Could that too.

    Part of the "Gift that Keeps on Giving" class. Nobody wanted to serve on them.
     
  10. timshatz

    timshatz Active Member

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    Read the same report. As the war was ending, the Brits were headed towards the American style carriers while the Americans were heading towards the British style carrier.
     
  11. Nikademus

    Nikademus Member

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    #11 Nikademus, Dec 3, 2010
    Last edited: Dec 3, 2010

    Not exactly. Victorious is considered a poster child for this but IIRC this was due to a postwar fire. Fire damage in general can kill the future career of armored and unarmored carrier alike. The Franklin...the ultra example of Essex survivability, never reentered full service.

    Given the heavier weight of bombs used and in some cases, number of hits, I don't doubt that the armored deck and hanger deck were instrumental in their survival, particularily Illustrious. While the armored box concept was flawed in that it helped contain the bast area and increase topside damage, it kept such damage topside. I would not want to be on a Lex or Yorktown class CV and get pummeled by 1000kg SAP bombs or even 500kg SAP.

    The Americans recognized the value of the armored deck and incorprated it into the Midway, but retained the "open hanger" concept which would allow blast effects to vent.
     
  12. RCAFson

    RCAFson Well-Known Member

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    #12 RCAFson, Dec 3, 2010
    Last edited: Dec 3, 2010
    According to Wikipedia, if you add up all the casualties suffered on all the RN armoured flight deck from all forms of attack, throughout the entire war, they still suffered fewer casualties than several USN carriers did individually from a single attack:
    Kamikaze - Wikipedia, the free encyclopedia

    Another interesting fact is that all USN carriers from the Midway class onward have/had armoured flight decks:

    (25) Cracknell, W.H, Cmdr USN, Warship Profile 15, USS Enterprise (CVAN 65) Nuclear Attack Carrier, p56.Comparison of armoured to unarmoured flight deck designs - Wikipedia, the free encyclopedia

    I did some research on this topic earlier, and the truth of the matter is that armoured flight decks had relatively little to do with the differences, in terms of aircraft capacity, with the different aircraft complement of the RN AFD (Armoured Flight Deck) carriers in comparison to their USN counterparts. The greater part of the difference is explained by the fact that the RN carriers had much more weight devoted to AA guns, and carried much more armour overall, and when built the first 4 AFD carriers all had their flight decks shortened due to "round downs" at either end, which shortened the useful length of the deck. The other major factor is that the RN did not use a permanent deck park in the early stages of the war and thus aircraft capacity was limited to hanger capacity. In the later stages of the war the RN began to use a permanent deck park and then they operated more than 50% more, larger and heavier, aircraft. Illustrious operated 57 aircraft in mid 1944 and flew off more than 50 aircraft during one strike. If Enterprise had operated according to early war RN doctrine, she would have only carried about 40 aircraft - her hanger capacity limit.

    Direct comparisons are misleading because the Yorktown class carried vary little armour and had a very light AA armament compared to an equivalent RN AFD carrier. In 1943, the only survivor, Enterprise had to be extensively reconstructed to handle the increasing weight of AA and heavier aircraft, The Essex class, OTOH, are much larger ships than the RN AFD carriers, and it is interesting to speculate what an RN design team could have come up with if they could build to the same weight.

    AFDs meant that the enemy had to attack the carriers with AP bombs, and these were much less destructive than SAP or GP bombs, especially if they near missed. Additionally the Luftwaffe used much heavier bombs to attack the AFD carriers, than the IJN used in the Pacific, but the negative aspect of this, from the Luftwaffe perspective is that the range of the attack aircraft was then severely reduced due to the heavy bomb load, unfortunately for the RN they were often forced to approach land to within even the short range of a JU-87, yet the AFDs still reduced the number of attack sorties that the Luftwaffe could fly against them.

    Lastly post war scrapping of RN carriers is proof of only one thing: That the UK was bankrupted by WW2, and it tells us nothing about how repairable the AFD carriers were or were not. The rebuild given to Victorious suggests that all the damage inflicted on the AFD carriers was repairable given sufficient resources, such as possessed by the USN.
     
  13. renrich

    renrich Active Member

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    Page 55, "British and Dominion Warships of WW2"-"The Illustrious class which followed-none were completed before the outbreak of war-introduced a significant innovation with an armoured hanger. The weight of armour, at such a height, entailed some sacrifise and only a single hangar was adopted with aircraft stowage reduced to 36." "The last three were altered to incorporate an additional half hangar aft but the thickness of the hangar side armor was significantly reduced to compensate."

    Victorious, an Illustrious class displaced 23000 tons. She carried a maximum of 36 aircraft and mounted 16-4.5 guns and numerous smaller guns. She could make 31 knots

    The Essex class displaced 27100 tons. They carried 100 aircraft and mounted 12- 5 inch guns and numerous smaller guns. She could make 33 knots
     
  14. RCAFson

    RCAFson Well-Known Member

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    What you don't mention is that total weight of armour increased over Ark Royal, and even if the same weight of armour was carried lower it would have still meant significant design changes over Ark Royal. However, Ark Royal is an interesting case in point, as she only operated with about 55 aircraft, because she did not use a permanent deck park, unlike the USN carriers.

    Victorious was operating with about 55 aircraft in 1944/45 when she used a permanent park. Implacable also carried 16 x 4.5in guns, displaced 23800 tons, had a speed of 32 knots and operated with 81 aircraft in 1945.
     
  15. RCAFson

    RCAFson Well-Known Member

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    Aside from the fact that the weight of the bombs reduced the operational range of the Luftwaffe aircraft, there is a very high probability that at least one the bombs that fell on Illustrious in Jan 1941 would have penetrated into her machinery compartments and crippled her, but for armoured flight deck. If this had happened, the RN would have had no choice but to scuttle her.

    I saw an interview with a Stuka pilot who participated in the attack on Indomitable and according to him, the bombs used were not AP, and thus there is a good chance that they would broke up on her armoured flight deck if they had hit it:

    View: https://www.youtube.com/watch?v=BcD51ribM5Y
     
  16. Glider

    Glider Well-Known Member

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    #16 Glider, Dec 4, 2010
    Last edited: Dec 4, 2010
    I served on the Hermes off Cyprus in 1974, so maybe not everyone was loath to serve on her:evil:
     
  17. Glider

    Glider Well-Known Member

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    Would the Yorkrown have been sunk by these hits. Clearly we don't know but my guess would be that she would have done. No other carrier from any navy in any situation survived from nearly as many hits from such large bombs. The interesting point is the value of the armoured deck. As pointed out the majority of the bombs didn't hit the armoured decks, by some bad piece of luck the lifts seemed to get hit a lot. I personally believe that the strength of the design came from the decision to treat the hanger as a magazine with double thickness sides, additional fire curtains, additional passive defences such as automatic sprinklers and structural strength. All these helped reduce the chances of a fire. If a fire did beak out it could be sealed and burn itself out due to lack of oxygen

    Where armour did help was in the Pacific against the suicide attacks. Not only were the thick decks able to cause more of the bombers to 'bounce' off the deck they also aided repair. If a US carrier was hit even if the damage was limited thee was an excellent chance that the deck would be holed taking time to fix. On an armoured deck the most that would normally happen would be a dent in the deck. This was easily and quickly repaired using what was basically quick drying cement.

    The major down side of a RN Hanger was that if despite all the precautions if a fire did break out and wasn't smothered the hanger acted like an oven and the temperatures would soar, going much higher than in a 'normal' fire. This could and I believe once did, cause significant structural damage
     
  18. parsifal

    parsifal Well-Known Member

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    I think all three of the big Navies had armouring schemes for their big carriers. For the Yorktowns, the Illustrious and the Shokakus they were all protected by an armoured deck, moreover the weight of the armour scheme was overall very similar for all these ships.

    What set the british ship apart was that whereas the main armour deck in the USN and IJN was low down, below the hangar, in the British carrier it was a box that surrounded the Hangar. Putting the armour deck to the side and above the hangar, raises the CG and affects stability, so the only option the British could adopt was to knock an entire deck of the ship and reduce the size of the hangar. The result was that even under the best of conditions the british carriers could only carry 45 aircraft, although in 1944 they adopted a deck park like the USN, which raised the CAG to 53.

    Comparing the Japanese and USN ships is interesting. The USN ships were the more balanced, IMO because they distributed the protection to both anti torpedo and anti bomb protection, whereas the Japoanese tended to concentrate more on vertical protection, below the waterline.
     
  19. freebird

    freebird Active Member

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    Parsifal, any thoughts on the armour vs wood for the #2 bomb impact?
    I winder if the 3" deck armour helped slow the bomb (although too thin to stop a 1,000 lb AP bomb) might have slowed it down a bit, enough to make it explode above the waterline? (instead of below)
     
  20. parsifal

    parsifal Well-Known Member

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    I dont know, hard to say. I always believed the 1000 lb/kg bomb hit was a 1000 lb and hit the armoured deck or the armoured lift.

    However I do think the Illustrious class were overall better protected than the Yorktowns. Given that the Illustrious almost sank as a result of these hits, one has to place greater doubt on the survivability of the Yorktown under similar damage.

    Thats about the best I can do i think.
     
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