CONFIDENTIAL REPORT 2G-21
S72
     
 
FORMER GERMAN SUBMARINE TYPE XXI
 
 
 
 
FIRE CONTROL EQUIPMENT
 
     
 
SUMMARY
 
     
          The vessel is equipped with two turrets in each of which two 30MM anti-aircraft guns are mounted.  
          Turret turning, gun elevation and firing are controlled by the gunner, using power obtained from the main hydraulic system of the vessel.  Controls are simple and directional.  The motors bear strong resemblance to a type of oil pump which has been removed from those U.S. submarines which had it installed because it was found unsuitable for the type of hydraulic oil used in U.S. Naval practice.  The motor is otherwise of interest from a mechanical viewpoint.  
     
     
     
     
     
     
     
     
 
July, 1946
 
 
 
 
PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H.
 
     
     
     
 
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  REPORT 2G-21
S72
     
  1.  General  
          The vessel is fitted with two turrets, one at each end of the conning tower fairwater.  
     
  2.  Turrets  
          Each turret is equipped with a twin 30MM machine gun mount, two pressure tight ready service tanks for 250 rounds each, a seat for the gunner, foot controls and related hydraulic gear for gun firing, and hand controls and related operating gears for gun elevation and turret turning.  
          There is a scuttle in the top of the turret, through which the gunner's head protrudes.  The forward face of this is protected by a shield which is interlocked with the guns and rises as the guns are elevated.  
          The turret is carried on a ball bearing race and the carrier ring on the fairwater is fitted with an internally toothed ring gear which engages the spur gear associated with the turning motor.  
          Stops are fitted to limit elevation to 90 degrees, and depression to 10 degrees, and to limit rotation to approximately 170 degrees each side.  The forward turret can be locked at 0 degrees relative, and the after turret at 180 degrees relative.  The guns are locked at 5 degrees depression.  
          The turrets are, according to the specifications, of the same special steel (Wsho/Mo) as the bridge armor plating, and of the same thickness, 17MM (.67 in.).  
     
  3.  Turret Control  
          There is a foot pedal below the gunner's seat, and a combination hand grip and hand lever at the proper elevation before him.  Operation of the foot pedal opens and closes ports in a piston valve, thereby connecting the hydraulic supply line to the trigger mechanism of the guns.  The hand lever, when turned in a horizontal plane, opens ports in a piston valve which  
     
 
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  REPORT 2G-21
S72
     
  controls the admission of oil to a hydraulic motor.  This motor operates through a reduction gear train to a spur gear which engages the ring gear aforementioned, and turns the turret.  By turning the hand grips of the lever in a vertical plane, ports on another piston valve are opened, connecting the hydraulic supply line to a second hydraulic motor which operates through a gear train to increase or decrease the angle of elevation as desired.  
          The turret, with its training and elevating gear, is very simple mechanically, and is understood to have been satisfactory except that the amount of hydraulic piping is excessive, the hydraulic operating units are exposed to sea pressure, flexible oil piping is required, and the result has been that the hydraulic turret gear has been the major source of contamination of the hydraulic system with salt water.  
     
  4.  Hydraulic Motors  
          The hydraulic motors employed are different from those used elsewhere in the vessel.  They are in general similar to the Healy-Shaw pumps, but have seven pistons, eight ports and a four-leaf cam face.  
          There are two piping heads to the motor, either of which can be supply or return line.  Each pipe connects to four ports on the cylindrical face of a column projecting into the casing, and the four ports for one pipe alternate with those for the other pipe about the cylinder.  A wheel with seven cylinders opening radially outward rotates on the column, which acts as an axle.  In each cylinder is a piston to the outer end of which is connected a pair of wheels turning on ball bearings.  A spring is inserted between the cylinder head and the piston head.  
          The pump is so arranged that when oil is admitted to one line it has an open path, by reason of the arrangement and location of the ports on the column and the wheel, to one or more cylinders.  Pressure of the oil forces the piston outward, and the face of the cam contributes a vector tending to rotate the wheel. When the piston reaches the end of its stroke as determined by the cam face, the supply port is closed, and when the cam starts to push the piston back toward the center of rotation a return port is opened,  
     
 
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  REPORT 2G-21
S72
     
  permitting evacuation of the oil from the cylinder.  With the porting and pistons provided, there are 28 power strokes per revolution.  
     
  5. Comments  
          Controls are simple and directional.  To turn the turret the gunner merely turns the handlebar the desired direction.  To raise or lower the guns he merely tilts the handlebar in the desired direction.  
          The motors are believed to be appropriate for the oil employed, and provide a more compact power unit than the IMO type motors used elsewhere in the vessel.  
     
     
     
     
     
     
     
     
     
     
     
     
     
 
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