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

Mort Hans -December 10, 2012

Commentary by Senior Technical Editor, Steve Taranovich

There are a plethora of technical articles showing designers how to develop good circuits and systems reliably, but there exist very few that outline the possible pitfalls, difficult design compromises and the thought process that goes into decisions to take one direction over another at a design crossroad.

The following discussion, research and analysis by Mort Hans, brings to light the events and history leading up to a design to meet a need by the WWII military to provide a critical product for their bombers.

It is an unusual story because it’s not about a successful program, but an unsuccessful one. Unsuccessful, probably primarily because of its complexity and unreliability. Thanks to Hans’ research and tenacity to find people who tested and were involved in the design, he has pieced together a great tutorial to which all designers need to take note.

Part one of this article will cover the Introduction and background of the project, the bomber platforms for which it was designed and the Sperry Central Station Computer and the P-4 Computer outline.

Part two will delve deeply into the P-4 Description and analysis of impending problems, restoration at the CAM (Cradle of Aviation Museum), Appexdix and summary of the Fire Control System.

We want to again thank the CAM, Josh Stoff (Collections Curator) and Mort Hans who have a rich history of Long Island’s part in aviation history displayed. Hans also has a collection and memories of his broad background experiences as a designer which he has eagerly shared with EDN’s readers over the last year like the Slideshow: Slide rules and charts - a personal collection and Aircraft simulator challenges at the Cradle of Aviation Museum

When in the Long Island NY area, it would be worth your while to visit the Cradle of Aviation Museum It’s an awesome place for children and adults. Fly an actual simulator, visit the JetBlue Sky Theater Planetarium or just enjoy a tour of Long Island Aviation with one of the expert volunteers made up of many former engineers and experts who worked in the aviation industry.


When The Cradle of Aviation Museum (CAM) first acquired the Sperry Gyroscope Company’s P-4 analog computer in the spring of 2004, my goal was to find out what it was and then to prepare it for display.  At first glance, with its periscope sights, it seemed that it belonged in a naval museum’s display of a submarine’s conning tower rather than in an aviation museum’s display of a World War II computer and gun sight. 

As I began to research the origin of the P-4 analog computer, I learned that (a), the computer was originally designed as part of a central fire control system for the remote control of bomber gun turrets primarily for the B-29 and B-32 bombers to be built by Sperry and General Electric (as backup) and that (b), ultimately the Sperry contracts were cancelled and the production contracts awarded to General Electric (GE). 

I was curious as to why the Sperry contracts were cancelled so I added finding out as another objective.  In a corporate brochure, The Story of the Sperry Corporation, the reason for the cancellation was attributed to the (Air Force’s) decision, to adopt local stabilized control, without mention of the technical problems or unsatisfactory performance of the turrets and periscope sights.    

When this report was originally completed in February 2005, I was unaware that the Sperry Central Station Computer System had been the subject of a case study by the Air Force.  The Sperry system, it turns out, was one of a number of case history studies commissioned by the Air Force after the close of World War II.  Their purpose was to examine various Research and Development (R&D) projects conducted by both the Air Force and its contractors based on reviews of original project documents.  No information could be found as to how a case history was selected.  Were they only failed research and development projects?   

Or, were they also selected in terms of the lessons to be learned in order to improve the outcomes of future R&D projects?

A microfilm copy of the Sperry system case history, compiled by the Historical Office, Air Force Materiel Command, at Wright Field was obtained a month after the report was written.  The case history, 257 pages in length, consists of three parts: a summary of the overall project referencing original documents, a summary of the contents of each referenced document and a copy of the original file documents. The report isn’t dated, but one security declassification page is dated January 17, 1950. 

After reviewing the Sperry Case History File, I thought it would be instructive to add a new introduction to my original report and to include the case history summary as an appendix.  This would permit the reader to see for himself the importance of working from source material, whenever possible, rather than relying on dimming memories and material published at a much later date; in this instance, a half-century later.  I thought it would also be helpful if some of the key facts in the summary were presented at the beginning so that the reader would have a reference in seeing for himself how facts and events sometimes change over time in their retelling.  Thus, the differences between the conclusions in my original report and the facts as they emerge in the case history would be apparent.   

Next: Key facts

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