Auxiliary power distribution circuit layout installed on this type of vessel corresponds in general with the circuit layout incorporated in the type IX-C40 vessels.  
March, 1946
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  REPORT 2G-21
  (a) Introduction
  (b) Description
  (c) Conclusion
  (d) Report 2G-21-S62-1
  (e) Report 2G-21-S62-2
  (f) Report 2G-21-S62-3
  (g) Report 2G-21-S62-4
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  REPORT 2G-21
          (a)  Introduction  
                  Reference should be made to Report 2G-9C-S62 on type IX-C40 vessels and to the German Instruction Books "Skizzenbuch Band E Typ 21" (Sketch Book, Band E Type 21) and "Schiffnetz und Verbraucher U Boote Typ XXI" (Ship's Circuits and Auxiliaries U-Boat Type 21) regarding the power distribution circuit installed in type XXI vessels.  The scope of this report is concerned only with the differences in the two systems.  
          (b)  Description  
                  In order to more clearly understand the installation in this type of vessel a knowledge of the battery installation contained in Report 2G-21-S62-4 is necessary.  
                  The system provides for connection of the auxiliary power distribution circuit to any of the six pre-divided battery groups.  This is accomplished in the following manner.  Under normal conditions all auxiliary equipment installed forward of the Engine Room is energized through the forward distribution board located in the control room which by means of a transfer switch can be connected to battery group 1.1, 1.2, or 1.3 while auxiliary equipment in the Engine Room and aft is energized from the after switchboard located in the Maneuvering Room which by means of a similar transfer switch can be connected to battery group 2.1, 2.2, or 2.3.  Provision is made to cross connect these power supply circuits by means of disconnect blocks so that the after switchboard can be energized from the number one battery groups or the forward can be energized from the number two battery groups.  Double fusing of circuits apt to be in use during a dive or while submerged is not employed as is the case on type X B vessels.  
                  Several discrepancies exist between the actual installation and the circuit layouts in the German Instruction Books.  These are enumerated as follows:  
                  (a)  The designed power supply for the auxiliary power distribution boards contemplated use of groups 1 and 3 of each battery.  As previously described the auxiliary power switchboards can be energized from any of three groups of each battery.  The forward switchboard, number 2, being energized from groups of battery  
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  REPORT 2G-21
  number 1.  The after switchboard, number 1, is energized from the groups of battery number 2.  
                  (b)  The designed 120 V power supply for the creeping speed motors (These motors may be operated at 360 V or at 120 V) provided for use of a transfer switch at the motor which permitted connection of the port motor to group 2 of battery 2 or to the after auxiliary power board which as described above permitted connection of the board and hence the port creeping motor to group 1 or 3 of battery 2 whichever is connected to the board at the time.  A corresponding circuit was designed for the starboard creeping speed motor, the forward auxiliary power board and the groups of batter number 1.  The transfer switches at creeping speed motors are not installed.  The motor is connected to its auxiliary power board which in turn is energized as described under (a) above.  
          Several criticisms with regard to location of circuit components are presented.  It is to be kept in mind that the disconnect blocks provided for connecting switchboard number 1 to the groups of battery number 1 and of switchboard number 2 to the groups of battery number 2 are not installed under normal operating conditions.  
          (a)  The after switchboard, number 1, is located in the Maneuvering Room.  The transfer switch and disconnect blocks are located in the Control Room along with the forward switchboard, its transfer switch and disconnect blocks.  This same grouping of components exists on type IX-C vessels.  In the event of a casualty in way of the control room a possibility of losing all auxiliary power exists.  
          (b)  The main fuses between battery groups 1.2 and 1.3 and the transfer switch are mounted in a common fuse box.  A similar box exists for battery groups 2.2 and 2.3.  Both of these boxes are mounted on the forward side of the forward control room bulkhead practically adjacent to each other.  A similar condition exists in the crew's quarters with regard to the fuses from battery groups 1.1 and 2.1.  This type installation is considered very poor in that a localized casualty in these areas might well mean complete loss of all auxiliary power at a critical time.  
          (c) Since each creeping speed motor is energized from the applicable auxiliary switchboard, the fuses for the particular motor are mounted in that board.  In the case of the port creeping speed motor this is satisfactory  
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  REPORT 2G-21
  since it is energized from the after switchboard which is located in the same compartment.  However, the starboard creeping speed motor is energized from the forward board located in the Control Room and the circuit's only fuses are located there.  In the event these blow during a critical operating period, additional confusion will exist in that either personnel will have to travel from the Maneuvering Room to the Control Room or an additional burden placed on the ship's phone circuit in order to have Control Room personnel make the change.  
          (d)  The same criticism stated in (c) for the starboard creeping speed motor is true of the starboard main motor ventilation blowers.  
          (e)  In addition to the above criticisms, it is felt that the auxiliary power component layout in this type vessel with regard to accessibility for the necessary operation of the component is inferior to the other types of German submarines being evaluated.  This is evidenced by the following examples.  In the Engine Room several manual controller mechanisms for auxiliaries are installed outboard of the Main Engines, in a rather constricted area.  To operate these controllers it is necessary to clamber on top of the main engines, then while lying on top, to actuate the controller.  
          The same conclusions as are contained in report 2G-9C-S62 with regard to the application of circuit components, practices, design etc. apply to the type XXI vessels.  However, in light of the system installed in type X B vessels, it is surprising that some of the more desirable features incorporated in that type vessel are not installed in this later type vessel.  The criticisms offered arise not from the German's need to conserve critical materials, but rather from poor planning on his part.  
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