The German vessels had no permanently installed searchlights, nor were pressure-proof outlets provided on the bridge structure.  
          Provision for use of portable 20 centimeter (7.9 inches) and 35 cm (14.2 inches) searchlights was made as follows.  From outlets provided in the Conning Tower, the cable attached to the light and the light were led through the bridge hatch, being long enough to allow the operator to take any desired position on the bridge.  
          The 20 cm signal unit was designed to suspend from the operator's neck by means of a canvas strap.  The weight of this units was 9.5 pounds as compared to 23 pounds weight of the USN 8" portable unit.  
          Contributing to the difference in weight in favor of the German unit are the following factors:  
                  (a)  The housing is made of aluminum (or other light weight metal).  
                  (b)  The simplicity of the shutter mechanism which consisted of a piece of 3/32 inch wall thickness phenolic tubing 2-1/2" in diameter and 4" long actuated by a simple lever mechanism.  
          The power supply for the 20 cm unit was 24 volts 50 cycle A.C. or 24 volts D.C. being obtained either through the use of a step-down transformer or a dropping resistor.  
          A switch was provided as an integral part of the unit to energize or deenergize the circuit as required.  The bulb used was a 100-watt incandescent type, silvered on the end to insure that all light emitted was reflected light as an essential requirement of  
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  type shutter mechanism used.  
          The shutter mechanism was operated with the right hand, while the switch was energized with the left.  In addition, a focusing device was provided for use of the right eye.  No left hand units were observed.  
          Plans available indicate that some type IX-C vessels were provided with the 20 cm and 35 cm light, while others were provided only with the 20 cm light.  There were no 35 cm searchlights available on vessels at Portsmouth.  The trend of the German on later type vessels was to provide an outlet for only the 20 cm signaling searchlight.  
          Tests of visibility and maneuverability were made on U-873 while on trials which place the unit in a very favorable position with regard to the 8" USN signal searchlight.  A paragraph of this report is reproduced here for record purposes.  
          "On a bright day with the sun not behind the sending searchlight, the German light may be used at a range of approximately 4500 yards without the aid of binoculars.  Under similar conditions the USN 8" searchlight can be read at a distance of about 2500 yards.  With a bright sun behind the sending light, the German searchlight can be read at about 1700 yards.  The USN 8" searchlight can be read at about 1300 yards under the same conditions."  
          For additional information regarding the operating characteristics of the German 20 cm unit as compared with the USN 8" and 12" signal searchlights, reference should be made to Enclosure (a) of Officer-in-Charge U-873 letter U873/866 Serial (44) of 8 April 1946.  
          Two 20 cm lights have been forwarded to the Bureau of Ships Code 660 for detailed study.  Reference should be made to the report to be written by that activity when it has been completed.  
May, 1946
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