C/Ws Robertson & Watson.
    Copy No. 171.
Top Secret.    
                    Current Order No. 81 - March 1944.
Distress Transmitting Gear for U-boat  "U-249".
Rubber Dinghies and Rafts. Rec. 18.7.44.
  Reg No:  Top Sec. 83.
  Encl.  -
  1)  Distress transmitting gear is provided for the transmission of distress signals from rubber dinghies or rafts.  Frequency 500 Kcs.  (600 metres).  Aerial load 8 watts on CW and 6 watts on ICW.  
          Range for communication with aircraft:  
  Audibility up to 450 Km.  
  D/F range up to 300 Km.  
          Range for communication with U-boats:  
  Audibility up to 450 Km.  
  D/F range up to 100 Km.  
  2).  An automatic transmitter can be used for distress signals.  It sends "S.O.S." and the alarm signal.  (12 dashes of 4 seconds duration, with a pause of 1 second between the dashes).  
          When distress signals are sent by hand, the position in latitude and longitude (Degrees and minutes as a four figure number) should be given, if possible, after the alarm signal.  
  3).  Times for transmitting distress signals.  
  a)  At 15-18 ad 45-48 minutes past each hour (International periods of wireless silence for picking up distress signals.)  During these times there is most chance of signals being received by ship or shore wireless stations.  
  b)  Distress signals should be transmitted frequently outside these times, if the coast is within 500 Km., or if other boats are in the vicinity.  
  c)  Even if the damaged U-boat has been able to transmit a war emergency report or a short signal regarding damage sustained, distress signals should still be sent, (in addition to the times stated in "a"), at least every 10 minutes, so that immediate salvage action may be expected and bearings taken on distress signals.  
  4).  Times for reception of distress signals.  
  a)  All outward bound ships at sea, in the North Sea, Norwegian waters, the Arctic, and the Mediterranean, and in the North Atlantic as far South as 35 degrees N., should switch on to receive, if conditions permit, every hour from 15 to 18 minutes and 45 to 48 minutes past the hour on 500 Kcs.  (600 meters).  
  b)  Outside this area, boats only listen if there are other boats within a radius of up to 500 Km.  
  c)  If a boat has picked up a distress signal, a continuous receiving watch should be set.  The receipt of a distress signal is to be reported immediately by short-wave wireless message, together with the true bearing and signal strength of the signal, and the position of the receiver.  All boats within a radius of 500 Km. of the boat reporting should immediately set a continuous receiving watch on 500 Kcs.  Boats receiving distress reports should transmit these, as stated above, by wireless message.  


    C/Ws Robertson & Watson.
  6).  Technical notes:  
  a)  Transmitter is watertight.  It can therefore be put overboard along with the rubber dinghies or rafts.  
  b)  Kites or balloons are provided, to carry the 65 metre aerial.  Balloons should only be used with a wind strength of less than 6 seconds a metre.  Above this and in doubtful cases, the kite should always be used first, so that the balloon is kept ready for periods of calm.  Balloon should be inflated to a diameter of 1 metre.  If the balloon is over are (guaranteed age is stamped on the balloon), it should only be inflated to 90 cm. and two balloons should be attached to the aerial.  In cold weather balloons soon shrink after inflation.  Refilling is necessary, therefore hydrogen generators should be kept until completely exhausted.  Balloon will last from 1 to 1-1/2 days.  The rise of the kite can only be greatly facilitated when the wind is slight by pulling in and freeing the aerial wire.  
  c)  All distress transmitting gear is provided with a description and working instructions for the box of accessories.  
  d)  4 "Aphrodite" balloons are always to be kept with the set ready for use, as substitutes for worn-out balloons.  These balloons must be periodically exchanged for new ones.  
  f)  The transmitter should be tested for working efficiency each time the boat leaves harbor, and after long storage.  



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