The Engineering Book: From the Catapult to the Curiosity Rover: 250 Milestones in the History of Engineering

1939

Norden Bombsight

Carl Norden (1880–1965)

If the Air Force wants to drop a bomb precisely onto a target today, the bomb is equipped with a set of fins that can be adjusted by a computer connected to a GPS receiver and inertial guidance system. Before the bomb is dropped, the computer receives the latitude and longitude of the target. As long as the bomb releases anywhere in the general vicinity of the target, the bomb will hit that target precisely.

Now let’s get into our time machine and travel back to the 1930s. There are no GPS satellites. Yet, with World War II being fought in Europe, there is a need to drop bombs from airplanes and hit targets as accurately as possible. To solve this problem, Dutch-American engineer Carl Norden developed the Norden bombsight, which was introduced in 1939.

Before the bombsight’s inception, airplanes dropped gravity bombs with no guidance systems. The gravity bomb followed an arc once the airplane released it. The arc’s exact shape was controlled by the plane’s speed and heading, the wind’s speed and heading, and the altitude of release. Therefore, there is an exact place and time when the airplane needed to drop the bomb during the bombing run. The Norden bombsight gets the plane to the right place and calculates the right time so the bomb arc precisely intersects with the target.

Given the lack of microprocessors, this was not a trivial problem. The Norden bombsight used two systems: a gyro-stabilized platform to keep the bombsight level during the bombing run, and a mechanical computer to do the calculations. The key to the effectiveness of the mechanical computer was the user interface. After initial setup, the bombardier would put the target in the crosshairs and then adjust knobs so that the target stayed in the crosshairs without any drift. The mechanical computer would then release the bombs at the right time.

The Norden bombsight had a great advertising campaign associated with it once its top-secret classification was removed. It was never as accurate in real-world situations as claimed publicly. But given the technology available, it was a remarkable piece of engineering.

Pictured: A view through the Norden bombsight.