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Hedgehog

Discussion in 'Submarines and ASW Technology' started by denny, May 22, 2015.

  1. lwd

    lwd Ace

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    On the other hand there were a number of vessels in the Pacfic that were seriously damaged by near misses both bombs and shells. With HE it is generally the shock wave/over pressure that does the damage rather than fragments. An underwater explosion produces a shock wave that can be damaging at greater distances than the same explosion in air. In any case the request was for a comparison. The information provided was designed to facilitate that. One would have to presume similar if not identical circumstances to readily compare the probable damage but without them being specified a comparison of the explosives seamed to me to be the best I could do. The question of whether the barges are a useful analog is also rather an open one. I'm not at all surprised that they were fairly resiliant to such damage. Being shallow draft and I suspect somewhat flexable would have mitigated a lot of the effects of a shock wave. A sub on the other hand can find even a fairly small leak to be quite dangerous.
     
  2. phylo_roadking

    phylo_roadking Member

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    ...as were vessels in, say, the Norway campaign in 1940, "damaged" by near misses. When you drill down however, you often find that seriously damaged meant damage to exterior but still vital fittings like rudders and chains, or damage to hull plates outside the armour belts. One German destroyer headed home from Norway before landing her part of a landing force after heavy seas stoved in hull plates ;) A hull plate doesn't actually need to be catastrophically holed to be seriously damaged...just parted from its neighbour(s)...

    Yes, the underwater explosion creates a pressure wave that propagates further than in the air - via the water as a transmission medium - hence my point that the larger the explosion I.E. the larger the actual charge/burster charge...the better in comparison to the weight of any casing/container. As it's the explosion and pressure wave that does the physical damage, not the "propelled material" as the same transmission medium absorbs the kinetic energy of casing fragments etc.

    A small leak in a submarine can indeed be quite dangerous - but the actual danger depends on the depth and the overall pressure already on the sub's "pressure vessel". Thus a charge like the Hedgehog adds its pressure to the water pressure already applied to every square inch of the pressure vessel.

    There's also possibly the issue of OVER-pressure.....but whether it was fully understood in WWII as yet, before the advent of nuclear weapons, is debateable...and the ability of nuclear weapons to create a pressure wave so strong in relation to the vacuum behind it, that as the pressure wave passes over a hardened target - a sub's pressure vessel being a perfect example...that the atmosphere INSIDE the pressure vessel tries to break OUT to fill the vacuum. It does happen with conventional explosives; it just requires very large explosions devices to create such a large pressure wave and accompanying vacuum.


    (in relation to the Sealion barges - they were actually far less flexible thanks to the alterations carried out by the Germans in the summer of 1940. See my comments elsewhere regarding how the changes - extra bracing, pouring steel rail-reinforced concrete into the bilges etc. actually helped them EXCEED the KM's original mandated standards of seaworthiness and sea states they could cope with. My point was how close conventional iron bombs had to come to do catastrophic damage by fragments/puncturing hull plates because of how the water absorbed the kinetic energy of bomb fragments.)
     
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  3. lwd

    lwd Ace

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    I wonder if the Sea Lion barges would actually have been more vulnerable to the concussive force of bombs detonating under water near them than the barges the RAF used to as test cases. If much of the foce goes into lifting or bending the barge(whether it springs back or not) then catastrophic damage was unlikely but a more ridged barge might have had a greater tendency to break rather than bend.

    By the way my interpretation of the original question was how would a hit from a hedgehog compare to one from a bomb or a shell. Little or no way to really compare the effects of an AP shell that hits compared to a hedgehog IMO the others would suggest the sub would have to be fairly shallow to make a comparison. Of course depth charges and HE bombs might be more comparable but speed of detonation could have some considerable impact here.
     
  4. denny

    denny Member

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    Wow...that theory of "Over Pressure" is interesting.
    I never would have guessed that, but my knowledge of physics is not quite at the Nobel Level :)
    Those poor, German, sub guys. Didn't they suffer something like a 70%-80% loss of men.?
     
  5. Triton

    Triton New Member

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    3 out of 4 died. Most from 1943 onwards.
    Basicly, the U-Boats were successful as long as they could attack on surface at night. The advantages were clear, the Boats were as fast as the corvettes and Sonar was useless, a skilled commander could choose the most attractive targets from a convoy. Some stayed hours in between the ships.
    With the introduction of Radar on the escorting vessels, they had to change to conventional submarine-warfare and the efficiency dropped. But with a lot more subs and improved tactics, they still maintain dangerous.

    When Huff-Duff, Hedgehog, Long Range Bombers were available, the conventional Type VII - Boats were rendered obsolete and they were only still in use to keep the Allies busy. Leaving the port with a conventional submarine was almost a suicide mission. Very primitive radar detection sets or the Schnorchel and new torpedos were only small improvements on the situation.
     
  6. Takao

    Takao Ace

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    You could also add centimeter-wavelength radar, airborne radar, escort carriers, more escorts, improved sonar, improved anti-submarine tactics, etc.
     
  7. Triton

    Triton New Member

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    Yes. Or the Leigh-Lights. Airborne radar was crucial, when the "Atlantic-Gap", the area without air cover, was closed, warfare with conventional boats was almost impossible. In 1944, the german subs could hardly leave their bases in France, they were attacked in shallow waters in the Biskaya. Unbelievable that the Luftwaffe wasn't even able to protect an outgoing or incoming U-Boat for few hours with a few fighters.

    Dönitz tried out a lot, the U-Boats were fitted out with as much anti-aircraft guns as possible and/or left the bases in groups. But U-Boats are very bad platforms for any type of artillery.
     
  8. Takao

    Takao Ace

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    Yeah, Dönitz's "stand and fight" order did not work out as well as he expected.

    Even though the Germans fitted as many AA guns as possible on U-Boats, they still were quite limited in the number of mounts fitted, and these could be easily overcome by a coordinated attack by British Coastal Command ASW planes.
     
  9. Triton

    Triton New Member

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    The U-Boats with serious AA-equipment, the so called "Flak-Fallen", were successful - but only for a short time. Later on, the ASW planes attacked in groups or simply stayed out of range until the sub dives. And it has to dive or will be attacked by destroyers called by the Coastal Command.

    When leaving the bases in groups, the first U-Boats dived and were protected by their "escort" on surface, but the last one was likely to be killed so no commander wanted to be the last one to dive.

    The only way to solve the problem would have been air cover by fighters.
     
  10. harolds

    harolds Member

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    This is another example of Goring's poor performance. He gave minimal help to the Kriegsmarine-the only force that had the ability to harm the allies at a strategic level. Inter-service cooperation with the Heer was good but with the KM it was abysmal. Off topic, but I can't pass up a chance to bash Goring-and by extension, Hitler. ;-)
     
  11. lwd

    lwd Ace

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    What could the Luftwaffe really have done to help the KM significantly?
     
  12. harolds

    harolds Member

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    They could have kept the long-range liberators and Sunderlands off the backs of the U-Boats for quite a few miles of ocean and given them a good chance of surviving their first dive of their trip. A few bombers could have distracted or perhaps even hit the RN destroyers in the Bay of Biscay.
     
  13. Takao

    Takao Ace

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    From this map over on u-boat.net: http://uboat.net/maps/biscay.htm
    It looks like the majority of the U-Boat losses would be at the end of or beyond the range of the Me-109G, although the FW-190 likely could have made the escort flight.

    Inconsequential.

    Only three of the many U-boats lost in the Bay of Biscay during 1943 were due to surface ships.
     
  14. Triton

    Triton New Member

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    More long range reconnaissance planes would have helped too.

    A radar set on the boats would have been essential to avoid air attacks anywhere. It is true, improvements for the subs to avoid attacks were possible, but thats not the point. U-Boats weren't built to control the sea but to attack and attacks with conventional dive boats, that were dreadfully slow submerged, remained difficult and extremly dangerous.
     
  15. lwd

    lwd Ace

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    Sounds good on paper but how many fighters would need to be tasked with this duty? Then there's the problem that if they only fly CAP over the Uboats they give away the Uboats location. As I recall a rule of thumb for CAP was that if you wanted to keep x fighters on CAP duty you need 3x fighters and that's if the range from field to CAP location is short. Remember also that British radar could track planes over the Bay of Biscay to some distance from the British shores. Looks to me like this is going to require a significant diversion of LW resources where are they coming from?

    When does it become reasonable to insert these into the construction cycle? Since Germany was rather resouce short where are the resources coming from?

    The problme with this is if they use the radar they are likely to be detected and localized. At the very least this means targets are routed around their location but it could also mean ASW assets are sent to their location. There was a limit to how long they could stay submerged. The radar horizon would be pretty close with a sub as well.
     
  16. Triton

    Triton New Member

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    Didn't the US-Navy uses Radar on their boats?
    But I agree, the use of Radar isn't the best idea when the ocean is completely controlled by the enemy. Early in 1941 during "Rheinübung", Admiral Lütjens didnt use Radar for the same reason.

    The FW 200 Condor was used with success, so it is likely, that more planes would lead to more success. To sink a supply ship with a lot of ammo, tanks, planes or fuel is the most effective way to victory.
     
  17. Carronade

    Carronade Ace Patron  

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    German fighter support would mainly have been long-range types like Ju-88s targeting the Liberators, Catalinas, and the like that were such a plague to the U-boats. Donitz also had hopes that the He-177 would prove effective in the air-to-air role; some models had forward-firing 20/30mm cannons. I suspect that rather than literally flying CAP over U-boats they would conduct long-range searches for Allied ships and convoys and hopefully inflict attrition on whatever Allied planes they encountered. I recall a few incidents of Ju-88s encountering antisubmarine aircraft or bombers/transports transiting between England and Gibraltar.

    The Luftwaffe had a few successes against Allied antisubmarine forces in 1943 with the new Hs-293 guided bomb, including sinking the sloop Egret and badly damaging the Canadian destroyer Athabaskan.
     
  18. Markus Becker

    Markus Becker Member

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    Carronade beat me to it.
     
  19. gtblackwell

    gtblackwell Well-Known Member Patron  

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    Black May: The Epic Story of the Allies' Defeat of the German U-Boats in May 1943
    Aug 9, 2011
    by Michael Gannon

    This is an excellent book, to me, for those interested in this thread. I am nearly through reading it on Kindle which I paid $7,.99 but now it is 17.99 ????? Paperbacks at $.99. It covers a Westward bound convoy of ships in ballast and their escorts. It gives keen descriptions of how submarine warfare was conducted, specific tactics, weapons of all types, aircraft, It describes the development of depth charges, how close they must be to be effective, how hedgehogs work, the thickness of pressure hulls in millimeters, the effectiveness of type 7 and 9 boats, etc. Endless information. Then it covers the Bay of Biscay during the same period, how various radar systems worked, describes specific attacks, etc. It is taken from both Allied and axis war time and post war accounts. I highly recommend this factual book about the turning point of the U-Boat war.

    Gaines
     
  20. Gromit801

    Gromit801 Member

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    With the invention of the Mk.24 Fido, TBF's would carry two 500 lb bombs, and a pair of Fidos. The 500 pounders were used mainly to force the U-Boat to submerge (though a lucky hit was always a possibility), allowing the TBF to drop a Fido in the sub's wake. The Fido had a much better kill record.

    Hedgehogs were in a sense, like taking the tracers out of a fighters ammo belt. If you missed, you didn't alert the prey, and could set up for another attack.
     

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