F.d.U./B.d.U.'S War Log

16 - 30 April 1940

PG30263

     
 
 
 
Date
Position, Wind, Weather
 
and
Sea State, Illumination,
Events
Time
Air Pressure, Moonlight etc.
  
 
 
 
 
K r i e g t a g e b u c h.
 
B. d. U. - Op.
     
     
16. - 30.4.
     
1940
   
16.4.
           At 0410 a report was received from U 47 that she had found the transports at anchor in Bygden (Vaagsfjord).  4 misses!  U 65 had already fired a double shot (most probably at close range therefore) without success.  I am now beginning to suspect that even the use of impact firing is not preventing torpedo failures.  Either the G7e is keeping a much greater depth than hitherto known or the pistol does not arm.  A second report from U 47 confirms this idea:  in a second attack on the transports another 4 torpedoes failed to fire.  This means a total of 8 unsuccessful shots by our best U-boat commander.  It is quite clear to me that these failures are responsible for the commanding officer's lack of success.
          I requested immediate assistance from C-in-C Navy by telephone and made a corresponding T/P to Supreme Command of the Navy, giving a list of failures during the last few days.  I requested the Director of the Torpedo Inspectorate to come to Wilhelmshaven tomorrow for a discussion.  U 47's reports shows that it was right to leave the boats in the Vaagsfjord in spite of the high risks.  It was only in the south of the Vaagsfjord that they were able to regain contact with the transports.  But now that U 47's attack has failed and will be followed by a corresponding anti-S/M activity on the part of the enemy.  It is necessary to get the boats out of this witches' cauldron and dispose them at the entrance to the Anden fjords.
          Reports from U 25 and U 46 confirm my view that things are very difficult for the boats in the fjords, as they have no means of attacking destroyers; an "AZ" shot passes under the destroyers, and "MZ" shot detonates prematurely.  The short, light nights and a sea as smooth as glass add to their difficulties.  I am therefore withdrawing the U-boats from the Namses and Romsdale fjords as well as from the Vaagsfjord to positions off the fjords.
   
 
          In reply to her radio message 2100/15/4, received 0948/16/4, U 46 has been ordered to return.
 
   
 
          The Trondheim position, which was not occupied yesterday, is occupied again.
 
   
              U 46 and U 51 are interrupting their return passage and have been given new positions as they still have torpedoes left.
 
   
 
          Group FOELLA has joined the groups mentioned yesterday, between Lofoten and Narvik.   U 57 has been ordered to the position off Scapa and further U-boats are to go there.  After Kristiansand was occupied, I sent Lieut.(s.g.) Windler, the Flotilla Engineering Officer, with additional personnel, cypher material etc., to fetch U 21.  U 21 is now fit to proceed and dive and can sail from Kristiansand today.  Lieut.(s.g.) ROESING has inspected the Norwegian S/M's and reports that they are unfit for use either operationally or in the U-boat school.  Further details remain to be seen; I have made the organization department responsible for finding and requisitioning Scandinavian S/M's.  U 13 reported the sinking of a Tribal class destroyer N. of the Shetlands, so the "MZ" has worked in this area. This points to Zone setting O being being responsible for premature detonators.
 
   
 
          U 26 and U 43 are to be converted for patrol transport when they get back.  U 32, UA, U 101, U 122 are already being adapted for this purpose.
     
 
 
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Date
Position, Wind, Weather
 
and
Sea State, Illumination,
Events
Time
Air Pressure, Moonlight etc.
  
 
 
   
17.4.
           It becomes increasingly obvious that the failure of the torpedoes is the cause of our lack of success.  On 15.4:  U 48 reported misses and failures at destroyers.  U 65:  one double miss at a transport (Vaagsfjord).  U 47:  4 misses at transports lying at anchor (Vaagsfjord).  U 47:  1 G7a failure, 3 electric torpedoes failed to fire (Vaagsfjord), probably also at transports.
        These reports from the Vaagsfjord and Westfjord boats are depressing.  The hopes that things would be improved by switching over to "AZ" have proved unfounded. I have placed the most capable commanding officers at these vital points for the operation.  From their reports and from what is known of their personal qualities and abilities, there can be no doubt that they made determined efforts and tried everything possible.  I can only accept part of the shots as misses.  A large part were undoubtedly failures of torpedo or firing unit.
          Results have shown that it was a mistake to go over to "AZ".  The essential conditions were that the torpedo should not keep a depth more than 1.75 meters below that set and that impact firing should work for certain.
          These conditions are clearly not fulfilled.  The reason for the failures must be either that the torpedo runs considerably deeper and the targets are undershot or that, for some reason, the pistol does not fire or does not arm.  This suspicion of mine is increased firstly by the fact that the information which I have received from the responsible authorities on depth-keeping has varied considerably with time, so that I have the impression that there is no certainty on this point, and secondly by the fact that already in October and November odd reports were received from boats which indicated that shots had hit without an explosion following.
          This partly confirmed by information from the Torpedo Inspectorate.  U 65 and U 48 were fitted out with pistols with 4 bladed propellers.  It appears that these pistols are liable not to arm.  They too have been issued to the boats without adequate trial.
          The Director of the Torpedo Inspectorate visited me today with some of his assistants to discuss the failures during the last few days and the possible causes and remedies.
 
  The results of the conference were:
1) 10% failures to arm must be expected with 4 bladed pistols.  Due to an oversight, improvements which had already been recognized as necessary, were not made to these pistols.  This is a fresh, quite unjustifiable source of failures and it remains to be seen who is responsible.
2) The Torpedo Inspectorate does not consider it possible that the pistol fails to arm when switch setting "A" is made.
3) According to information given to the Torpedo Inspectorate by the hydrographer, magnetic influences on the pistol must be expected in the fjords.  But this influence need only be feared close inshore.  It could only be present in the open sea area if there are hitherto undiscovered layers of ore below the sea bottom and then only in depths
   
         
 
                            
 
 
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Date
Position, Wind, Weather
 
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Air Pressure, Moonlight etc.
  
 
 
   
 
  of water up to 100 meters.
4) The Director of the Torpedo Inspectorate is doubtful of the advisability of using impact firing with switch setting "A" as he does not trust the torpedo's depth keeping, and he strongly advised a return to "MZ".
5) Experiments with torpedoes with adapted depth-gear have been satisfactory on the whole so far.  Variations in depths were between plus or minus 0.5 meters.  Sufficient experiments have not yet been made, however, to give a final judgment.
        As a result of the conference the following instructions were given to the boats, in agreement with the Torpedo Inspectorate:
a) The G7e probably runs more than 2 meters below the depth set.
b) Boats in zone O are therefore no longer to use switch setting "A", but to fire with "MZ" except inside narrow fjords.  Danger of premature detonation is greater in these.
c) No fans with time switches are to be fired with "MZ", but multiple shots according to fire control memorandum or improvised fans with 8 second intervals.
d) With "MZ", set depth to equal draft, 4 meters against destroyers, 3 or 4 meters against S/M's.
e) With "AZ" set 4 meters, 3 meters in good weather.
        These instructions are so complicated that I would never give them to operational boats except in present circumstances.
 
18.4.
           Following Naval War Staff's new instructions 4654, boats are being distributed as follows:
 
A) Small boats:
  The following will go to the U-boat School as soon as possible:
  U 1 - 7, 9, 10, 18, 19, 20 and 21 - 13 boats
  The following will remain off Bergen until their supplies are exhausted:
  U 14, 17, 23, 24 - 4 boats
  Total 17 boats
  The following will remain for operations:
  U 13, 56, 57, 58, 59, 60, 61, 62.
B) Large boats:
  1) U 25, 38, 49, 65 will remain in the Lofoten area until they have used all their torpedoes.
   
         
 
                                   
 
 
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Date
Position, Wind, Weather
 
and
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Air Pressure, Moonlight etc.
  
 
 
   
 
  2)  U 30, 34, 50 will remain in the Trondheim area.
  3)  U 47, 48 37 are on their way back.
  4)  U 29 is on her way out.
  5)  U 46, 51, 52 are being recalled.
  6)  U 28 is under repair
  Total:  15 boats.
       The following are intended for transport to north Norway:
  U 26, 32, 43, 101, 122, UA - 6 boats.
        These will patrol up and down the NOrwegian coast at the same time.  Of these only U 26 is at sea, about to enter Trondheim.
        With these preliminary arrangements there will be:
 
8
   small boats
 
15
   large boats
 
23
   U-boats
  left for the main operation by the beginning of May, and the 6 transport boats will only be available to a limited extent.
   
          U 47, which was recalled owing to engine defects, is ready again and she has been ordered to the area west of the Shetlands-North Minch.  U 26 entered Trondheim.
   
          U 13 and U 61 have been ordered to put in to Bergen to refuel.  They are to operate again with U 57, 58, 59 and the first wave of the remaining small operational boats.
   
 
  U 37 has returned from patrol.  This boat also had premature detonators in zone O, but nevertheless sank 3 steamers, totaling about 18,600 tons, and a warship, probably a cruiser, with switch setting "A" or south of zone O.
 
   
 
          U 51 reported a double shot at a Southampton class cruiser, no success.
 
   
              Reports from U 52 and U 65 show again under what difficulties the boats are operating in the fjords:   almost no darkness, strong anti-S/M activity at times, reloading only possible by moving away.
 
   
 
          It is therefore correct to withdraw the boats in the Namsos fjord to positions further out.  U 34 and U 50 have been ordered to waiting positions off Folla, near the island of Kya.
 
   
 
19.4.
           All operational and tactical questions are again and again colored by the intolerable state of the torpedo arm.  The problem of where to operate the boats depends not only on the usual conditions, but in every case the question: "Will the torpedo work?" has to be considered.  The torpedo situation today is as follows:
          On 18.4 U 37 reported on her return that she had 2 prematures detonators in the area between the Shetlands and Iceland and had then scored successes with switch setting "A".  This is further proof of the fact that premature detonations do not only occur
   
       
 
 
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Date
Position, Wind, Weather
 
and
Sea State, Illumination,
Events
Time
Air Pressure, Moonlight etc.
  
 
 
   
  near the coast:  plainly the magnetic influence exercised on the pistol in zone O are not explained.  So far no premature detonators have been reported from the southern zones, on the other hand there have been 2 successes (hit on English S/M by U 3, hit on Tribal class destroyer by U 13).
        Torpedo Inspectorate informed us by telephone that investigations had shown that a further 7 boats were issued with the pistol with 4 bladed propeller from which 10% failures to arm are to be expected.  The boats are U 38, 43, 50, 52, 57, 61 and 62.  We will therefore have to take further failures due to non-arming into account without being able to do anything about it.  Efforts will be made to exchange the pistols in U 61 when she puts into Bergen to supply.  Arrangements are being made to fly the pistols to Bergen.
          On 19.4 in the morning the Director of the Torpedo Inspectorate telephoned that the results of trial firing showed that the G7e when set at 2 meters, kept a depth of 3.5-4.7 meters, i.e. up to 2.7 meters below set depth.
          My suspicions and the doubts expressed by the Director of the Torpedo Inspectorate on 17.4 on the torpedo's depth-keeping have thus proved well-founded.  I have therefore decided to let the boats leave the Vaagsfjord and Westfjord, as their operation there can no longer be justified.  Conditions are very difficult for those boats with the short nights (practically no darkness) and the narrow operations area, making it almost impossible for them to move away and the constantly recurring premature detonations mean great danger.  But in the light of this fresh information on the torpedo's depth-keeping it is no longer possible to go over the switch setting "A" as no targets with a draft of less than 5 or 6 meters could be torpedoed (the shallowest possible depth setting is 3 meters in good weather).  In effect, therefore, the boats are unarmed.
          During the night 19/20/4 U 47 reported 2 torpedoes fired at "Warspite" in square 5446 (about latitude of Namsos), which failed to detonate.  Range - 900 meters, depth 8 meters, zone minus 4, one end-of-run detonator.  U 65 reported a G7e premature detonator after 22 seconds at the cruiser "Emerald" in square 9741 (approach to Vaagsfjord).  In zone O (north of 62.5 degs. N), of 22 shots fired during the last few days at least9 have been premature detonators, which in their turn have caused other torpedoes fired at the same time to explode prematurely or to miss.  These premature detonators have occurred not only close to the shore but to a large extent, also in the open sea area.  The use of "AZ" with switch setting "A" is barred for reasons given earlier.
          At present, therefore, the Navy has no torpedo which can be used in the area north of latitude 62.5.  I am therefore, withdrawing the boas remaining in this area (off Andalsnes) in order to operate them to better effect in a suitable area south of this danger zone.  For shots against destroyers and submarines I have ordered a depth setting of 3 meters, which according to present knowledge and experience is the shallowest depth setting which leaves any certainty that the torpedo will not break surface.
          I was somewhat reluctant at first to take the Torpedo Inspectorate's advice and order a depth setting of 2 meters in good weather.  It is based on the fact that, with the 30 test shots mentioned, not one broke the surface when set at 2 meters, but these test shots were fired from an underwater tube from a depth of 4 meters and it
         
 
                               
 
 
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Date
Position, Wind, Weather
 
and
Sea State, Illumination,
Events
Time
Air Pressure, Moonlight etc.
  
 
 
   
  is questionable whether the torpedo will not break the surface if it is fired from a tube at 10 meters depth (depth of discharge tube when boat is submerged) with a depth setting of 2 meters, and what happens if the boat is down by the stern, which is not always avoidable when firing?  A surface runner, by day at least, is even more dangerous for the boat than a premature detonator.  On the other hand everything possible must be tried to eliminate under-firing.  I therefore, ordered U 30 to fire 2 test shots immediately from periscope depth with electric torpedoes, with a depth setting of 2 meters, one with the boat on an even keel, the other 30 stern heavy, and to report the result, giving the seaway.  The result was satisfactory, neither of the torpedoes broke the surface in a head sea 3.  I therefore gave the following order for depth setting of torpedoes:  Radio message 0103/21/4:
  In "MZ" shots, depth to equal draft minus 1 meter, against destroyers, submarines and steamers under 4,000 tons: depth 3 meters, in good weather 2 meters.  For "AZ":  depth 3 meters against all targets, 2 meters in good weather.
          The torpedoes fired by U 47 at "Warspite" on 19.4 which failed to detonate, are still unexplained.  I think it improbable that, with a depth setting of 8 meters, the torpedoes could have run under the firing field of a battleship, even if they actually kept a depth of 11 or even 12 meters.
          If these shots were not misses (which is highly unlikely in view of the commander's unmistakable report of failure to explode and the short range of 900 meters and a double shot), then it must be assumed that there was a degaussing effect.
          I consulted Professor Cornelius and Professor Gerlach by telephone and they consider that it would be extraordinarily difficult to fit D.G. gear in battleships and that it is therefore very unlikely in such ships at present.
          I am not quite convinced.  We have definite information that the English have fitted many of their merchant ships with D.G. gear for sometime past.  They will attach the greatest importance to the protection of their most valuable ships and make every effort to achieve it.  But for the few cases where a boat manages to fire at a large warship I would like, as far as lies in my power, to exclude the smallest chance of failure.  I therefore ordered, at midday on 21.4 a depth setting of 5 meters for shots at battleships.  Then, even if the torpedo runs 3 meters deeper, i.e., at 8 meters, impact firing may still take effect.  At the same time I restricted the use of the 2 meter shot to the G7e, as, with the G7a, there is still the danger of surface-runners.  During the last few days the boats have been overwhelmed with a large number of orders on the use of torpedoes, type of firing unit and depth-setting.  Resetting the pistols always means long re-loading jobs, which cannot always be carried out.  THe commanding officers are burdened and restricted by the frequent contradictory orders.
          I was forced to give these orders because of the constant fresh failures and the conclusions drawn therefrom, but, above all, by the almost daily new discoveries made by the Torpedo Inspectorate of the defects of their torpedo.  It now appears that the Torpedo Inspectorate had no reliable information on any aspect of the G7e.
          I had to do everything possible