The Norden Mark XV was an analog computer coupled to an autopilot and optical sight. The bombardier input altitude, airspeed, and wind. The mechanical computer—using cams, gears, and a gyroscope—continuously calculated the drop angle, accounting for gravity, air resistance, and wind drift.
It was classified "top secret" throughout WWII. Bombardiers swore an oath to protect it, and it was equipped with a thermite charge for destruction if the aircraft was shot down.