U-boat  "U249"            
  Rec. 6th Dec. 1944                                     84
  Reg No:  Top Secret 131.  
Top Secret.   Copy No. 171
Current Order No. 67 - Issued November 1944
  Firing torpedoes on the basis of firing data obtained by sound-detector.  
  I.  The captain can gain the best idea of the tactical situation by visual means.  The periscope is therefore the most reliable instrument for observation.  The captain should try to obtain his firing data by means of the periscope.  
  II.  Under present wartime conditions however, U-boats may find themselves in a situation where use of a periscope is impossible.  It is then a question of making the best use of the situation, if possible for firing purposes.  This is all the easier if the U-boat is equipped with sound-detector  apparatus and search gear.  Captain, who, are solely dependent, however, on the sound detector must be clear on the following possibilities of attack.  
  a)  U-boats can be in such a position that individual ships or convoys are passing overhead before they have had the opportunity of using their periscopes.  In this case it is considered possible to make a rough estimate of the general course, speed and range, using sound-detector and stop watch only.  The use of a "Zaunkönig" torpedo or a Lut-fan for attacking from astern, will, in such cases, have certain prospects of success.  
          Special attention must be paid to the following:  
  1)  The firing of torpedoes is up till now only possible from a submerged depth of 22 metres.  Therefore endeavours should be made to fire from a depth of 20 metres (for filling cartridges see front page note of TJ Book 2).  
  2)  As soon as it is suspected that a ship will pass overhead, an attempt should be made as soon as possible to estimate speed and general course in order that only slight alterations will be necessary when the ship is actually overhead.  
  3)  Stop engines when the ship is directly overhead and continue checking the range referring to the estimated speeds until the moment of firing.  
  4)  Prompt decision must be made by the Captain, which type of torpedo is to be employed (Lut of Zaunkönig).  
  5)  Directly after firing, the U-boat must dive to a greater depth (at least 50 metres), in order to avoid the possibility if torpedoes passing overhead, when traveling to a higher level.  (When firing Zaunkönig torpedoes, speed should not exceed 3 knots).  
  6)  Rapid grasp of the situation and speedy manipulation of the firing control apparatus and torpedo tube is absolutely necessary.  
  b)  If a ship does not pass directly above a U-boat, the firing data obtained by sound detector alone, are generally not sufficient to ensure the successful use of torpedoes.  
          The Captain is not in a position to judge by sound detector alone his position and range in relation to an individual ship or convoy.  It is not sufficient to know the enemy's speed only when firing a torpedo.  In spite of these inadequate particulars if the Captain has the impression that the situation is favorable, he should fire, if he foresees no further opportunities of attack during the operation, or for example when leaving the area of operation or when returning to base.  
                                                                                            Translated by C/W Watson  
                                                                                                                  C/W Robertson  



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