(typed in soluble ink)   Copy No. 135__
Standing War Order of the B.d.U. No. 173
Extracts from British Admiralty Notices.
1) U-boat decoys in convoys.
          U-boat decoys are to be employed whenever possible in convoys.
          They are to be placed among the rearmost ships, and under pretence of engine trouble, etc, must drop astern so as to attract attacking U-boats, lead them away from the convoy and then attack them themselves.
          Be suspicious therefore of vessels sailing behind convoys.
2) Procedure upon sighting the track of a U-boat torpedo.
          It is advisable, if circumstances in any way allow it, to drop one depth-charge immediately after sighting a torpedo-track.
          The purpose of this is as follows:
  1) The enemy submarine will imagine it has scored a hit, it will go to periscope depth in order to observe the result, and remain in the neighbourhood in the hope of being able to attack "the damaged ship" again.
  2) The detonation of the depth-charge marks the ship's position at the moment of sighting the torpedo-track and thereby assists any U-boat decoys that may be near.
3) English suppositions concerning the behaviour and deceptive devices of German U-boats with regard to English pursuit units.
    (Text of instructions to pursuit units)
  a) "We have reason to think that the Germans have not discovered our methods of finding U-boat positions, and that they believe these methods to be based on the listening principle.
            It is therefore possible that German U-boats, as soon as they realize they are being pursued, stop their engines and, whenever possible, go to the bottom.  Probably they only go on again when they think they are free of their pursuers, and then go first of all to periscope depth."
  b) "We have heard of two sorts of deceptive devices that may be used by German U-boats against U-boat decoys:
    These are:
    1) A sort of torpedo-trap, which leaves an oil track


    behind it, and thereby induces submarine chasers to follow a false trail.
    2) a device that can be thrown out by the U-boat, and which then, after it has proceeded a little way, emits noises like the propellers of a U-boat.
            While it would not do to suppose that these devices can be detected by position-finding apparatus, it is well to observe some caution in taking for granted the immediate presence of a U-boat in cases in which these phenomena have been observed.
            The commanding officers of all Asdic fitted craft are advised to be on their guard against these possibilities of deception.
            Observations on this score must be made and reported with all possible accuracy."
                                                      signed Dönitz.



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