Design hindsight from the tail-gunner position of a WWII bomber--Part two

The computer case is constructed of cast aluminum and finished in black crinkle paint, a common cabinet and panel finish for electronic and communications equipment during the 1930s and 1940s.   The case and panels showed minor wear with several dents and dings.  Two panel screw heads were missing with the screws still embedded.  Both periscopes showed corrosion in several places.  Internally, the wiring, shafts, gears, motors and electrical components, with some exceptions, were in excellent condition.  There were traces of what appears to be white mold.  Several switch contacts showed rust.  The elevation display mounted in front of the dorsal periscope was damaged and the pointer corroded. Overall, however, the periscopes and computer were in good condition and appear never to have seen service. 

The computer case measures approximately 29 ¾ x 12 x 20 inches.  Each of the periscopes is approximately 23 inches long and 5 inches in diameter.    From Figure 6 and a Sperry illustration in a corporate brochure, it appears that a periscope of the same diameter but approximately 38 ¾ inches in length was also made.  Periscopes of two lengths permitted the P-4 to be located in either the single or dual configuration at different fuselage locations with the shorter length used in the upper position as shown in Figure 6.  The overall weight with both periscopes is estimated to be 100-125 pounds.  In Figure 9 the periscope case has been removed to show the linkage to the sighting prism below the plexiglas cover. The wire in the periscope provides current to the heater imbedded in the collar around the sighting prism’s base. 

In Figure 10, the P-4 computer’s left panel has been removed to show both the mechanical linkages for the sight as well as the computing components of gears, cams and shafts driven by small motors.  The compartment on the lower right contains the rate gyro.  The gears and shafts are part of the drive mechanism that moves the periscope prism in azimuth and elevation in response to the gunner’s turning and rotating the control arms to track the target.

Fig.9. Periscope with case removed.