The Sight Unit Small Arms, Trilux, or SUSAT, is a 4×

telescopic sight A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a ''reticle'' – mounted in a focally appropriate p ...

, with

tritium Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...

-powered illumination utilised at

dusk Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before nightfall.''The Random House College Dictionary'', "dusk". At predusk, during early to intermediate stages of twilight, enoug ...

dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the diffuse sky radiation, appearance of indirect sunlight being Rayleigh scattering, scattered in Earth's atmosphere, when the centre of the Sun's disc ha ...

. The full name of the current model is the SUSAT L9A1. The sight is not designed as a

sniper A sniper is a military or paramilitary marksman who engages targets from positions of concealment or at distances exceeding the target's detection capabilities. Snipers generally have specialized training and are equipped with telescopic si ...

sight, but is rather intended to be mounted on a variety of rifles and to be used by all infantrymen. Similar devices include the

Advanced Combat Optical Gunsight The Advanced Combat Optical Gunsight (ACOG) is a series of prismatic telescopic sights manufactured by Trijicon. The ACOG was originally designed to be used on the M16 rifle and M4 carbine, but Trijicon has also developed ACOG accessories for ...

(ACOG), manufactured by Trijicon, and the Elcan Specter.

Use

SUSAT was the primary sighting system for the

British Army The British Army is the principal Army, land warfare force of the United Kingdom. the British Army comprises 73,847 regular full-time personnel, 4,127 Brigade of Gurkhas, Gurkhas, 25,742 Army Reserve (United Kingdom), volunteer reserve perso ...

's SA80 series weapons. It was also used with L108 and L110 light machine guns, and mounted to L7 and L111 machine guns. It was phased out and replaced by ACOG and ELCAN sight units during mid-life upgrade programmes. As of March 2025 it is still in use with much of the UK armed forces – primarily reserve, rear-echelon and for training use due to budgetary constraints. It is (or has been) also used by the armies of

Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...

Oman Oman, officially the Sultanate of Oman, is a country located on the southeastern coast of the Arabian Peninsula in West Asia and the Middle East. It shares land borders with Saudi Arabia, the United Arab Emirates, and Yemen. Oman’s coastline ...

Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...

and

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, 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 A reticle or reticule, also known as a graticule or crosshair, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the electronic v ...

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 An obelisk (; , diminutive of (') ' spit, nail, pointed pillar') is a tall, slender, tapered monument with four sides and a pyramidal or pyramidion top. Originally constructed by Ancient Egyptians and called ''tekhenu'', the Greeks used th ...

-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

-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 Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

. 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 Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

body, into which the eyepiece, objective

lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

and prisms are fitted as assemblies. The SUSAT sight was developed in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

by Royal Armament Research Development Establishment (RARDE) and is manufactured by United Scientific Instruments and Avimo, now known as

Thales Thales of Miletus ( ; ; ) was an Ancient Greek philosophy, Ancient Greek Pre-Socratic philosophy, pre-Socratic Philosophy, philosopher from Miletus in Ionia, Asia Minor. Thales was one of the Seven Sages of Greece, Seven Sages, founding figure ...

Optics.

Specifications

SUSAT L9A1 *Overall dimensions: (L x W x H): 145 x 60 x 55 mm *Weight: 417 grams *

Magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a size ratio called optical magnification. When this number is less than one, it refers to a reduction in size, so ...

: 4× *

Field of view The field of view (FOV) is the angle, angular extent of the observable world that is visual perception, seen at any given moment. In the case of optical instruments or sensors, it is a solid angle through which a detector is sensitive to elec ...

: 10 degrees (177 mils) * Objective diameter: 25,5 mm *

Exit pupil In optics, the exit pupil is a virtual aperture in an optical system. Only ray (optics), rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a optic ...

: 6.375 mm * Eye relief: 25 mm *Light permeability: >80% *Reticle illumination: Red tritium, glass ampoule *Illumination strength: Adjustable *Tritium ampoule lifetime: 8–12 years *Focus: −0.75 to −1.25

dioptre A dioptre ( British spelling) or (American spelling), symbol dpt or D, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, . It is normally used to express the optical power of a lens or curved mi ...

s *Operational temperature: −46 to +71

°C The degree Celsius is the unit of temperature on the Celsius temperature scale "Celsius temperature scale, also called centigrade temperature scale, scale based on 0 ° for the melting point of water and 100 ° for the boiling point ...

*Range Settings: 100 to 600 meters (SUSAT L9A1) or 300 to 800 meters (SUSAT L12A1) in 100 m intervals *NATO Stock Number (NSN): 1240-99-967-0947 (Sight Unit Small Arms Trilux (SUSAT) L12A1)

References

{{reflist

External links

United Scientific Instruments
��Official website
SIGHT UNIT SMALL ARMS TRILUX (SUSAT)
Firearm sights British Army equipment Military equipment introduced in the 1980s

Use

Reticle

Manufacturing

Specifications

See also

References

External links