Design hindsight from the tail-gunner position of a WWII bomber--Part two
Parts of the Sperry System were first installed on the B-17 for test purposes. Early reports revealed inadequate provision for keeping the air ion the computer and optical tubes dry, and probable inefficiency of the drive control and gun charger at low temperatures. The chief difficulty, however, was with the periscope sighting system, which had a limited field of view that locating targets was difficult.
The apparatus was so unsatisfactory that plans for the use of the Sperry System were changed in March 1942. Certain quantities of the B-29’s were to be equipped with the General Electric system, instead of the Sperry and direct sighting used in place of the periscopic. It was believed by the Experimental Engineering Section, Wright Field, that consideration should be given to making a like change in the B-32’s.
Considerable trouble was being experienced, too, in adapting the Sperry computer for use with the General Electric system in the B-28 type airplane. In view of these difficulties, Experimental Engineering Section, Wright Field, recommended that the Sperry facilities be converted to the manufacture of the General Electric system, then. Would be standard equipment for all types of airplanes requiring remote fire control.
At a conference held at Wright Field on ?? April 1942, it was definitely decided that the first three experimental B-29’s were to be equipped with the Sperry system, but that the production models would carry General Electric equipment. The 100 Sperry systems already under contract were to be procured as “insurance” – as standby, or alternate equipment. B-32’s were to use the Sperry system, with a change to direct (GE) sighting if that proved advantageous on B-29’s. No plans were made for the B-28’s, pending a decision as to whether this type of aircraft was to be produced.
A report from Elgin Field, Florida, where the Sperry XB-20 type system was being tested on the B-17C, was to the effect that the optical system and the spotting system needed changes, and that the whole system would not be effective at ranges over 500 yards if maneuvering was required of the plane while firing. It was believed, however, that these difficulties would be remedied, and that the system was basically sound.
Sperry informed Materiel Command, Washington, in November of 1942 that they had developed a target locating device that would overcome the difficulties that were being experienced with the periscopic optical sight. With this system, the target was located by direct vision. The computer operator then pressed a button which automatically directed the periscope at the target, and tracking and gun-sighting proceeded as before. Sperry asked that this device be tested in the XB-29, or in ships equipped with B-29 blisters.
Materiel Command, Washington, in a memo dated 16 November 1942 urged that this test be made and recommended, in the event the test was more satisfactory than comparative tests on General Electric equipment, that the Sperry system be substituted for the General Electric in B-29’s as soon as possible. The two systems were compared, to the advantage of the Sperry, as follows: (1) Sperry sights were power operated, and tracking was smoother than in the General electric manually operated system; (2) the double-sided periscope sights made it possible to cover the entire sphere from one sighting station, whereas side blister sighting stations could not pick up targets attacking initially from the opposite side of the plane; (3) the Sperry turrets were better adapted to easy maintenance; (4) Sperry was working on a sighting system that would make tracking and firing at night practicable.