SUSAT

The Sight Unit Small Arms, Trilux, or SUSAT, is a 4× telescopic sight, with tritium-powered illumination utilised at dusk or dawn. The full name of the current model is the SUSAT L9A1. The sight is not designed as a sniper sight, but is rather intended to be mounted on a variety of rifles and to be used by all infantrymen. A similar device is the Advanced Combat Optical Gunsight.
Use.
SUSAT was the primary sighting system for the British Army's SA80 series weapons and L108 and L110 light machine guns. It was phased out and replaced by ACOG and ELCAN sight units during mid-life upgrade programmes.
As of March 2019 it is still in use with much of the UK armed forces due to budgetary constraints.
It is (or has been) also used by the armies of Cameroon, Oman, Spain and Sweden, in assault rifles such as the Swedish Ak5B and the Spanish CETME LV, although after the replacement of the latter by the HK G36, those sights have been employed in Rheinmetall MG3 machine guns.
A similar unit known as the L2A2 SUIT Sight was used on the L1A1 SLR.
Reticle.
The reticle of the SUSAT is of unusual design. Unlike the traditional crosshair layouts commonly used, which are in essence a cross intersecting the target, the SUSAT has a single obelisk-shaped post protruding from the bottom edge of the sight. This type of reticle is sometimes referred to as the "German Post". This obscures the target at long range and the foreground. The reticle is tritium-illuminated for low-light condition aiming. The radioactive tritium light source has to be replaced every 8–12 years, since it gradually loses its brightness due to radioactive decay.
The L2A2 SUIT Sight uses a similar single post to the SUSAT, but protrudes from the top edge of the sight down to the middle of the field.
Manufacturing.
SUSAT is constructed from a one-piece, pressure die-cast, aluminium body, into which the eyepiece, objective lens and prisms are fitted as assemblies.
The SUSAT sight was developed in the United Kingdom by Royal Armament Research Development Establishment (RARDE) and is manufactured by United Scientific Instruments and Avimo, now known as Thales Optics.
Specifications.
SUSAT L9A1