Marking, labeling and designating were the result of considerable thought; and were conceived of as a basic principle applicable not only on board, but as well to sketches, manuals, stowage lists and all other related matter.  
          Circuit designation was simple and clear, and permitted use of smaller fuse and distribution boxes that would have been required if U.S. Naval designation had been employed.  
          The good features of the marking and labeling are deserving of consideration, although it must be acknowledged recommendation as to the adoption of the principle involved is beyond the scope of this report.  
March, 1946
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          Designating is in certain cases carried to greater lengths than is U.S. Naval practice, and in other cases is not as complete.  
  Class and Type  
          All German vessels were designated by class and type.  Submarines were designated by "U" (for "Unterseeboot", which is the German for "submarine") followed by a number.  The number gave no evidence of type, however.  
          Type numbers were associated with plans, instruction books and all other matter related to a given design.  For a complete list of types and related "U" numbers, see Naval Technical Mission in Europe Report No. 312-45 on submarine design.  
          "W" numbers were also assigned by builders, and will be found referred to on plans and in text material.  These numbers are builders' hull numbers, and refer neither to class nor type of vessel.  
  Marking Circuits  
          Circuits and piping are both identified, though not in a manner directly comparable with U.S. Naval practice.  
          Circuit marking follows the principles given below.  It is not self-evident, and requires use of the electric systems sketch book to trace circuits.  
          a)  Each unit is a given number, which appears on the unit, and in the table of connections for the fuse box serving the unit.  
          b)  If the name or the number of a unit is known, it is possible to refer to the tables in the sketch book and find from which box the unit is served.  
          c)  Having found the number of the box, the earnest seeker now goes to the box, on which is found an engraved plate with the circuit description code, the unit number in parentheses, and another number, or a word in that order, for each unit.  When the box is opened, the figure or word following the unit number on the cover is found painted between  
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  the fuses of the circuit serving that unit.  
          d)  To follow the circuit further, reference is again made to the sketch book, where it is found that the particular fuse box is served from a particular board in a designated compartment.  When traced back to the board, a set of fuses is found which bears the number of the particular fuse box.  
          e)  Any desired circuit can be traced back to the power source, or from the power source to the unit, in the manner described above.  The sketch book provides, in each case, a record of the cable size and type, and of the circuit fuse size.  
          f)  All references to circuits in text material on the different systems relate directly to the identification described above.  
  Other Units  
          Other marking is detailed in Submarine Painting Specifications (Austrichvorschrift für U-Boote) and in Color Codes for piping, bunkers, cells, tanks and pumps (Farbige Kennzeichung der Rohrleitungen, Bunker, Zellen, Tanks, Pumpen USW).  
          The system employs principle colors for basic identification purposes, with banding in other colors to provide detailed identification.  The secondary banding provided bears a general relationship to the basis code.  Colors are as follows.  
red Steam supply
blue steam exhaust
yellow fresh water
green salt water
brown bilge water
purple oil
black sounding , test and flooding
gray gas
          Examples of combination are as follows:  
red with purple band - steam line for bunker heating
blue with yellow band - condensate to feed water heater
yellow with two red bands - hot fresh water
green with purple band - cooling salt water to lub oil coolers, water jackets, etc.
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brown with green band - main drain piping
purple with blue band - lib oil purifying system piping
gray with brown band - L.P. blow
gray with two brown bands- H.P. blow
          On board the vessel, piping is marked in accordance with the established code, at intervals of not less than one meter (3.28 ft.).  Each mark is at least 150 mm (5.9") long, and where second color banding is provided, banding consists of one section of basic color 60 mm (2.36") long at each end, with intermediate bands as necessary, each of which is 30 mm (1.68") long.  
          Valves are marked with the same color code as the piping.  Where a valves separates two piping systems, is is marked with both codes.  Extension rods and shafts not fitted with handwheels are also color painted.  
          Direction of flow in air ducts is indicated by arrows:  red for supply, blue for exhaust, green for air conditioning and lavender for ozone in refrigerators.  A block across the arrow shaft indicates an emergency line.  
          The specified color codes are used not only on board ship, but as well on sketch book pages and in instruction books.  Further, the coding in instruction and sketch books is extended to include color identification of the different tanks, containers and of certain compartments, and of the different pumps.  
  Additional Types of Identification  
          Further identification is provided at handwheels on valves.  Wheels for hull closures all have a large ball cast on the rim.  Valves for seawater lines are balanced cranks with straight handles.  For fuel oil, balanced cranks with tapered handles are provided.  Lub oil handles are five-sided.  Fresh water and hydraulic system valves are five-clover type.  Compressed air system valves are circular, with the rim slightly raised above the hub, with three spokes, and with an oval rim section.  The exhaust gas blow system valves also have three spokes, but the rim is greatly offset from the hub, and the rim is a flat oval.  Emergency vent valves have three spokes, a U-section rim and a hand grip.  Hand gear for vent valves has similar wheels with five spokes.  The main H.P. blow valve handwheel is a large flat wheel with five spokes.  The main H.P. blow valve handwheel is a large flat wheel with five spokes, and the main L.P. blow valve is similar, with three spokes.  
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          Positions of cocks are indicated by grooves on the end of the square stern head.  
          An engraved plate is provided for each unit of any consequence, giving its name or number.  All valves, hull fittings, containers, lockers, fuse boxes, controllers, switches etc. are so marked.  Practically everything on board has its own label, and all tables interlock with sketch books, instruction manuals and stowage lists, as appropriate.  All keys have tags identifying their purpose.  
  Distinguishing Marks  
          Distinguishing marks are confined to those apparent from the design, i.e: the characteristic shape of the bridge and fairwater, the shape of the stern, and the cutaway superstructure forward.  On later vessels, superstructure and fairwater shapes have been changed, but remain such as to be easily identifiable.  
          Numerals were not in evidence during the war, but were at other times painted on both sides of the fairwater.  
          No historical data plates have been found, and no reference to such plates has been discovered.  
  Draft Marks  
          Draft marks are provided, but the locations are not identical on all vessels, as some vessels have no forward draft marks, but marks approximately amidships in lieu thereof.  
          Draft marks are measured up from the bottom of the keel.  Single numbers are painted each decimeter, and thence is a single horizontal line at each odd "0" and a double line right and left of each even "0".  Numbers and meter marks are either screwed or welded to the structure.  
          Marking, labeling and identification are complete, and of such character as to greatly simplify the work of learning the boat.  Attention is invited to the extent to which touch identification has been carried.  
          Electrical circuit identification, once the principle is recognized, is simple and effective, and has one advantage over the current USN practice, i.e: the elimination of  
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  large labels in fuse and distribution boxes eliminates the labels as determining factors in the size of such boxes, and permits a notable reduction in box size and weight.  Further, the interrelationship existing between instruction books, sketch books and circuit designation is such that only one text reference is necessary instead of the multiple references required in U.S. Naval practice.  
          The use of color codes on piping only where such piping is visible simplifies the painters' work, in that all piping can be painted the same color as adjacent surfaces, and special coloring can be confined to parts of the piping where it is of value.  
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