Drift Sight
![A Mk. I Drift Sight mounted on the side of an Airco DH.4. The lever just in front of the bomb aimer's fingertips sets the altitude, the wheels near his knuckles set the wind and airspeed.](/Images/godic/202501/10/Drift_Sight_Mk._I_on_DH41708.jpeg")
![Labelled diagram of the various parts of the Mk. IA sight. The wires making up the sights for timing the drop are just visible, while the directional wire at the bottom is not.](/Images/godic/202501/10/Drift_Sight_Mk.IA_diagram1708.jpeg")
The Drift Sight was a bombsight developed by Harry Wimperis in 1916 for the Royal Naval Air Service (RNAS). It used a simple mechanical device to measure the wind speed from the air, and used that measurement to calculate the wind's effects on the trajectory of the bombs. The Drift Sight eliminated the need for a stopwatch to perform this calculation, as on earlier devices, and greatly eased the bomb aimer's workload.