Drift Sight, Tail, RAF Mk IV Kit Ref No 1846/40, 21584 1940

Here is a WWII-era Tail Drift Sight, Mark IV Kit, as used in bomber and transport aircraft of the British Royal Air Force with navigator aircrew, such as the Avro Lancaster, and likely used in other bombers such as the Vickers Wellington and Short Stirling. This is a complete set that includes the optical periscope, base plate, two aluminum drift plates that screw onto the base plate, an electric cord for illuminating the sight, and wooden carry case with leather strap.  The original lamp is installed but unlikely to work. The remnants of a replacement lamp are stored in its recessed position in the case.  Made in England by Ottawa & Toronto Instruments Ltd.  Stamped on the side of the periscope is Ref No. 1846/40, indicative of a year of manufacture of 1940. The periscope would be positioned to view the terrain directly below the fuselage while in flight. The angle of flight is then aligned on the sight.  As the terrain passes below the aircraft, it travels at an angle that direct