1940 to 1949: Computing During World War II and the Postwar Era - The Technical and Social History of Software Engineering - page 63

justments using two control wheels. The time required for the analog computers to
perform their calculations was about six seconds.
The Norden bombsights were complex devices that used gyro stabilization to
ensure a level platform. The accuracy of the bomb drops using the Norden bomb-
sight was within 35 feet for best results and about 75 feet for average results. This
is not smart bomb accuracy, but it is not bad for iron bombs with marginal aerody-
namic qualities.
In a trial run using an obsolete battleship as the target, about 50% of the bombs
dropped from 4,000 feet using the Norden bombsight hit the target. Older bomb-
sights had less than a 20% hit rate under the same conditions.
During actual combat operations, the results from the Norden bombsight would
be less successful. This is because combat bombing during the war moved to much
higher elevations to avoid ground fire. Some B17 bomb runs were made from
more than 25,000 feet, while some B29 bomb runs were made above 30,000 feet.
Norden realized that feedback was needed between the bombsight and the air-
craft autopilot, so he developed an improved form of autopilot with a direct link
to the bombsight. This was called the Stabilized Bombing Approach Equipment
(SBAE), and this was also a form of analog computer.
The Royal Air Force approached the United States in 1938 about acquiring the
Norden bombsight but was rebuffed. In fact, they were rebuffed several times, and
the situation reached a point where in 1938, Neville Chamberlain wrote a person-
al letter to President Roosevelt, but this still did not achieve a transfer of Norden
bombsights.
Technical cooperation between the United States and Great Britain almost
came to a standstill because of U.S. reluctance to provide the Norden bombsight
to the Royal Air Force. The United States was concerned that if the Norden bomb-
sights were used in British planes over occupied Europe, their design might be-
come known to the Germans if any planes were shot down.