The Telescopic Sighting System (TESS) was a sight used on the FV4201 Chieftain tank[1] and RAF F-4 Phantom aircraft.[2]
The TESS was trialed and introduced in the early 1980s originally as a tank sight for the FV4201 Chieftain. Surplus stocks were used on F-4 Phantom aircraft operated by the Royal Air Force as a cost-saving measure for a long range daytime target identification device, whereas the United States Air Force used the TISEO on their F-4 Phantoms. The TESS was installed in the rear cockpit in the centre window section for the Radar Intercept Officer to use.[3] It was boresighted to the aircraft weapons system and when locked on target, the target was magnified six times.[4]