Bomb Release Control-Intervalometer, Type AN-B3
The Bomb Release Control (Intervalometer) permitted a bombardier to control the number of bombs dropped per release and their impact spacing. This would be used to set up a carpet bombing run, for example, over a large railroad marshalling yard, vs a more concentrated drop over a specific site such as a ball bearing factory. The left dial selected the spacing interval between bombs at a given airspeed, while the right dial selected the number of bombs to be released at a time. The bombardier could also choose to either manually drop the cache or automatically in 'train'. Used in most US bombers during WW2.