Bombsight

A bombsight is a device used by military aircraft to accurately drop bombs. Bombsights are a feature of combat aircraft from World War I on, first found on purpose-designed bomber aircraft, and then moving to fighter-bombers and modern tactical aircraft as these aircraft took up the brunt of the bombing role.

A bombsight has to estimate the path the bomb will take after release from the aircraft. The two primary forces during its fall are gravity and air drag, which make the path of the bomb through the air roughly parabolic. There are additional factors such as changes in air density and wind that may be considered, but these are only a concern for bombs that spend a significant portion of a minute falling through the air. These effects can be minimized by reducing the fall time through low-level bombing or by increasing the speed of the bombs. These effects are combined in the dive bomber. However, low-level bombing also increases the danger to the bomber from ground-based defences, and accurate bombing from higher altitudes has always been desired. This has led to a series of increasingly sophisticated bombsight designs dedicated to high-altitude level bombing.

Since their first application prior to World War I, bombsights have gone though several major revisions. The earliest systems were iron sights that were pre-set to an estimated fall angle. In some cases these consisted of nothing more than a series of nails hammered into a convenient spar, lines drawn on the aircraft, or visual alignments of certain parts of the structure. These were replaced by the earliest custom-designed systems, normally iron sights that could be set based on the aircraft's airspeed and altitude. These early systems were replaced by the vector bombsights, which added the ability to measure and adjust for winds. Vector bombsights were useful for altitudes up to about 3,000 m and speeds up to about 300 km/h. Starting in the 1930s, mechanical computers with the performance needed to "solve" the equations of motion were incorporated into the new tachometric bombsights, the most famous being the Norden. Later in World War II, tachometric bombsights were often combined with radar systems to allow accurate bombing through clouds or at night. When post-war studies demonstrated that bomb accuracy was roughly equal when optically or radar guided, optical bombsights were generally removed and the role passed to dedicated radar bombsights. Finally, especially from the 1960s on, fully computerized bombsights were introduced, which combined the bombing with long-range navigation and mapping.

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