Copy No. 171
Top Secret.
U-boat  "U 249"
    Recd.     5th August 1944
  Reg No.  Top Secret 92
    Encl.      ----
Current Order No. 62 of July 1944
  The use of a double torpedo conduit system when Schnorchelling  
          With regard to the exceptional prevailing conditions of pressure in the boat during a cruise when schnorchelling, in order to avoid torpedo failures or deflections as the result of a partial vacuum and much greater fluctuations of pressure, instructions are as follows:  
  1)  Before loading the torpedoes into the tubes, on principle ventilate the depth gear pocket when atmospheric pressure exists or for a normal pressure 1013 mb.  After loading, beware of gastight closing of the firing tube.  During the Schnorchel cruise set the equalising gear exactly at "Firing".  
  2)  After the Schnorchel cruise and adjustment to normal pressure conditions in the boat, set the equalizing gear to "Tube ventilation".  
  3)  Since, as a result of possible diminishing of the Schnorchel, stronger fluctuations of pressure are to be reckoned with, avoid re-charging the electric torpedo batteries on account of the danger of escape of battery acids.  
  4)  It has been the custom repeatedly to put the battery door lids, near the opening of the torpedo for the purpose of independent ventilation of the electric torpedoes in the reserve stowage.  This is forbidden since also here escaping battery acid can lead to deterioration in insulation value.  In future it is to be observed that the battery doors remain shut fast and the electric torpedoes only ventilated by means of the constant ventilation gear.  



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