Top Secret.
Copy No. 171
  U-boat  "U 249"
    Recd.     26.3.44.
Current Order No. 44 of March 1944.
Reg No.  Top Secret 32
    Encl.      ----
  1)  "Wanze" 2 overlaps the Radar range of the enemy from roughly 1.2 to 1.8 m. and allows visual and acoustic watches to be kept.  
  2)  When the enemy reaches "great L" location appears on the visual indicator as an erratically rising and falling curve of small dimensions, which steadily grows as the enemy approaches.  Curves of short duration, are, in most cases, due to interference.  
  3)  When the enemy, using Radar, reaches "small L", secondary traces may appear close to the main horizontal traces; this phenomenon, sloping outward like a roof, nearly always indicates an enemy "small L", and with it immediate danger for the boat; but it does not however always appear, and is therefore not a reliable indication of enemy "L".  
  4)  Combat experiences have shown that the alarm ranges of "Wanze" are sufficient in all cases, for the boat to submerge in time, or for the boat to decide upon an alternative course of action.  These alarm-ranges depend of the altitude of approaching aircraft and extend slightly beyond the comprehensive ranges of enemy sets.  Tests with captured Radiolocation gear, have in the Baltic, resulted in the following alarm ranges for visual reception with running engines:  
                  Altitude 2000 m. - range approx. 60 km.  
                  Altitude     50 m. - range approx. 10 km.  
          Effective ranges according to combat observation are, however, presumably slightly greater.  
  5)  Acoustic reception with stopped engines is better than visual reception.  If it is not clear whether a small curve is a location or is due to interference, acoustic reception with stopped engines can be carried out for short periods in order to improve observations.  
  6)  Sensitivity of visual and acoustic reception with running engines is approximately equal.  Acoustic reception with running engines is, in the long run, less tiring than visual reception.  At the first moment of location a regular rattling appears in the rhythm of revolutions of the "Wanze" motor.  The sensitivity of "Wanze" generally increases with a diminishing number of revolutions.  
7)  As far as possible, accurate differentiation between interference and actual locations is necessary, and interference from own electrical gear, including W/T sets, Cypher "M" etc. are to be analysed and watched.  Before starting up apparatus causing such interference, a report should be sent to FuM control.
  8)  Inherent radiation by "Wanz 2" is below calculable measurement and is of no consequence.  
  9)  In case of defect, in the Wanze set, install the "Borkum".  Output of this set, when the detectors are clear, is about 1/4 that of "Wanze".  



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