U-Boat equipment.....

Discussion in 'The War at Sea' started by chipm, Oct 2, 2020.

  1. chipm

    chipm Well-Known Member

    .......well, not just U-Boats, but any submarine.
    Were they able to tell what was around the boat while they were submerged.?
    If they were 50 meters down, were they able to tell if they were approaching some obstacle that was protruding from the sea bottom.or did they just have to rely on charts?
    Thank You
     
  2. Robert-w

    Robert-w Banned

    I think the simple answer was no they were effectively blind and working on touch but running on batteries they moved slowly anyway.
     
  3. Blutto

    Blutto Banned

    Sonar is the first thing that comes to mind.
     
  4. Robert-w

    Robert-w Banned

    Yes but very limited then
     
  5. Orwell1984

    Orwell1984 Senior Member

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  6. Dave55

    Dave55 Atlanta, USA

    From what I've read the key was to get as accurate a fix as possible immediately before diving with sextant, stars, landmarks on shore etc and then to keep track of compass heading and speed via stop watch so that you'd still know where you were. Then you could track your location on charts. A good navigator was key. Sonar too, as Blutto mentioned.

    They could also use their sextant or celestial navigation at periscope depths.

    EDIT: Posted before I saw Orwell's excellent post
     
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  7. chipm

    chipm Well-Known Member

    Thanks for (all) of the responses.
    Yeah, i was wondering how advanced their "Sonar" was, circa 1943..... or if they were just kind of blind, and assumed the submarine was operating (unless they were close to shores) in depths that never really presented any substantial Obstacles or Threats.
    Thanks Again
     
  8. Harry Ree

    Harry Ree Very Senior Member

    When submerged and under attack by anti submarine escorts and the like....set for silent running or stop and check for surface activity by listening to the noise being generated by surface vessel props.As regards any use of asdic (sonar) type of equipment,it was possible to hear the pings hitting the submarine,s hull.

    There would be charts and the skipper and navigator would route the optimum safe course for the task.In some waters such as the Baltic it was easily to run aground if charts were inaccurate,navigation was under performed or by enemy action a submarine was forced into shallow water.Shallow waters off East Jutland,such as the led to the capture of HMS Seal in early May 1940 which was intercepted by the Kreigsmarine while undergoing mining operations.Her skipper was able to destroy his asdac (sonar) equipment and destroy his code books before the boat was captured disabled,after a day of Kreigsmarine and Luftwaffe counter attacks.

    A good example of navigation and and a successful accomplished operation is to follow HMS Submarine Tuna as she approached the mouth of the Gironde to surface and launch Major Hasler's RM party of canoeists.Their task under Operation Frankton was to row down the Gironde and destroy enemy shipping in Bordeaux harbour using limpet mines.The skipper aided by charts navigated his path to the mouth of the Gironde submerged to avoid Kreigsmarine patrol boats whose operational activity was known to the RN.HMS Tuna approached the mouth of the Gironde from the south west, continually using the Cordouan lighthouse as a fix on his port and land on his starboard to arrive at the planned position for Mayor Hasler to launch his canoes.

    A problem for both RN submarines and those of the Kreigsmarine was that the waters of the Med were clearer to view in depth than other seas.The effect of this was that submarines submerged at periscope depth were likely to run the risk of being located by surveillance from the air.

    Maximum submarine depth of WW2 submarines was approximately 300 feet which was specified to avoid overpressuring of the boat hull.
     
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  9. Robert-w

    Robert-w Banned

    The main reason why a U boat submerged was to conceal itself. A sub until after WW2 was essentially a torpedo boat that could submerge if needed and indeed the first USN subs were officially classed as submersible torpedo boats. They spent the majority of their time on the surface. Indeed U boat attacks on convoys at night were usually launched on the surface the boat diving after releasing its torpedoes to avoid retaliation by the escorts. In such a situation operating any form of echo location device (like active sonar) would be lunacy as it would be picked up by the escorts' hydrophones. Likewise pinging merrily away whilst approaching ships in an anchorage would also be likely to be rewarded by depth charges. The USN started using active sonar in submarines only in 1945 for mine detection to allow penetration of the Sea of Japan which was heavily mined and nine subs were so equipped. Passive sonar (and the Germans had some very good stuff) which was widely used in U boats would be useless for underwater navigation. Scanning sonar which is a form of active sonar that gives some sort of picture of the surroundings was not developed until post war.
    A successful attack at below periscope depth into an anchorage would require a lot of pre attack reconnaissance, some very good charts as a result, brilliant dead reckoning and a lot of luck. It could be and was done
     
    Last edited: Oct 3, 2020
  10. Ewen Scott

    Ewen Scott Well-Known Member

    While that was true of British and US submarines at the start of the war, German U-boats were designed for deeper diving which they exploited. The early Type VIIA/B boats could dive to 220m (722 feet). This was gradually increased until the Type VIIC/41 increased this to 250m (820 feet). Type VIIC/41 - U-boat Types - German U-boats of WWII - Kriegsmarine - uboat.net

    It was a common tactic for them to try to avoid depth charge attacks by going deep (600 feet plus) and quiet and listen to the depth charges exploding above them. It was a bit of a surprise when the British captured U-570 in August 1941, put her into service as HMS Graph and they discovered her true diving depth. That led to modifications to depth charges.

    The later US Balao class had a 400 foot diving limit while the British A class, designed in 1943, pushed that to 500 feet.

    Given that your average submarine was about 200-300 feet long it didn't leave much room for error in shallow waters.
     
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  11. Blutto

    Blutto Banned

    That's a very good question and one I haven't found a huge amount of info on. Most articles focus on the use of sonar/asdic to detect submarines, rather than on submarines using it to detect other vessels and obstacles. ASDIC was a First World War initiative, so I'd like to think that by 1943 it had come on a bit.
     
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  12. chipm

    chipm Well-Known Member

    I think that covers all of it quite well..... Thank You
    VERY Interesting BTW :)
     
  13. Robert-w

    Robert-w Banned

    Submarines made extensive use of passive sonar - effectively hydrophones which could pick up and locate the direction of noise generated by ships (engines, prop wash etc) unlike ASDIC no ping was generated. The later U boats had rows of 'phones so that cross bearings could be taken and range computed. All well and good for target acquisition but no use for navigation unless the obstacle generated noise. Active sonar in subs a post war development especially with the development of the hunter killer, by this time the 'ping' was quieter and less likely to give away one's own position
     
  14. Robert-w

    Robert-w Banned

    And the Hedgehog was contact not depth fused
     
  15. Ewen Scott

    Ewen Scott Well-Known Member

    There is a difference between what the Allied submarine sonar equipment fitted in the WW2 era was capable of (active and passive) and how it was used in practice (largely passive). The Germans relied on their superb passive hydrophone arrangements.

    From Brown's "Nelson to Vanguard" about RN submarines and Asdic/sonar.

    "Experiments had been carried out with an experimental Asdic set in H32 in 1923 and a set was fitted in Oberon [completed 1927]. A much improved installation was fitted in the Odin class. It was originally intended for use as an active set, for attacking enemy submarines submerged. However, use in the active mode disclosed the position of the submarine and it was usually used as a passive, listening set as which it worked unexpectedly well".

    And in relation to the development of the T class
    "It was also thought likely enemy anti-submarine action would mean attacking at long range, possibly on Asdic information alone, without exposing the periscope. This suggested that a numerous bow salvo of at least eight tubes was needed in order to score hits by 'shotgun' effect."

    Under general wartime changes he notes
    "Asdic. All boats had the 129 set at the fore end of the ballast keel but this was blind above and astern. In 1943 the 138 was fitted on the after casing despite difficulties in squeezing the gear into the engine room".

    I also found this about the British Type 129 set in WW2. Seems it was capable of use actively and passively and an underwater communications device. You need to get down the page a bit to get to the WW2 bit. The History Of British Submarine Sonars

    And from the US perspective. Hydrophones, Sonar, and Other Listening Gear - Fleet Submarine - WW2
     
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  16. Ewen Scott

    Ewen Scott Well-Known Member

    Correct. So it had be launched accurately to secure a hit. The deeper the sub the more opportunity for a miss due to the increased sink time, and without the benefit of the blast effect of the depth charge to compensate. So missing by a few inches was as good as missing by a mile.

    That is why the RN developed the Squid mortar. It threw 3 charges ahead of the attacking ship in a triangular pattern which exploded at the depth set, just like a depth charge. It performed even better when 2 were mounted. When viewed from above the pattern generated was hexagonal, but there was a difference in depth settings between the two mortars. The idea was that the sub would be caught between two triangular layers of exploding charges. Its use was linked to a depth finding sonar, Type 147, to increase its accuracy.
     
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  17. chipm

    chipm Well-Known Member

    Wow, that is something i did not know.
    It is a rather important "Detail"...... :)
     
  18. Ewen Scott

    Ewen Scott Well-Known Member

    And just to put the some context to this discussion. Against a sub at 600 feet the length of time it takes for a weapon to reach that depth from the surface is

    Standard British Mk VII depth charge - 60 secs.
    Heavy Mk VII depth charge - 36 secs
    Hedgehog bomb - 26 secs
    Squid - 14 secs.

    To that needs to be any time the projectile spends in the air from the DC thrower, or mortar. Add in the fact that the normal max setting on a DC was 300ft in the early war period increasing to 500ft later you can begin to see just how difficult it was to kill a deep dived U-boat. To ensure a kill it was estimated that a MkVII DC containing 290lbs of explosive needed to explode within about 20/26ft (depending on the type of explosive used) of the sub or double that to force it to the surface. A Squid bomb with 207lbs of explosive, was effective down to 900 ft, but would need to go off a bit closer for the same effect.

    A U-boat creeping along at 1.5 knots to avoid making noise, travels 50 yards in each minute.

    So you can begin to see why Squid was so effective as a result of being able to significantly shorten the engagement time while giving the U-boat less time to escape the critical blast zone.
     
  19. Robert-w

    Robert-w Banned

    Perhaps a minor point but it isn't the blast that does the damage it's the pressure wave The primary danger from a depth charge explosion is the pressure wave itself, not the bits of debris it throws around. In World Wars I and II, naval ships detonated bombs near submarines to compromise their structural integrity and key instruments. Initial blast damage was rarely fatal, but the power of the underwater pressure wave was debilitating enough to force targets to surface, opening them to direct fire.
     
  20. Robert-w

    Robert-w Banned

    According to the Barrow Submariners Association ASDIC in British subs in WWII was never switched to active mode. mainly for the reasons I expressed in an earlier post - it would give them away. Submariners recognised that active sonar might be useful as a means of communication in an emergency but otherwise wanted nothing to do with it.
     

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