THE TRILUX INFANTRY SIGHT UNIT
A New Small Arms Sight for the Infantry (Article/Advertising Infantry (Article/Advertising info by MAJ W.J.G. Hancook.)
In the last thirty years there have been many improvements in military Rifle design. With few exceptions, Rifles are now automatic or semi-automatic, they fire a more powerful bullet, make use of lightweight materials and are manufactured with modern production techniques. One aspect of Rifle design, however, has changed very little over the years and that is the sighting system. Apart from the introduction of the aperture ring to replace the old V notch backsight, the sights in use today would not be unfamiliar to a soldier of one hundred years ago. To have lasted so long these conventional sights must have a lot to commend them—and they do. They are cheap, simple and robust and are a reasonable compromise between the demands of extreme accuracy and quick, battle shooting; but as any flustered recruit on the range knows only too well, the problems of trying to focus the backsight, the foresight and the target, all at the same time, takes a great deal of practice to get right. Conventional sights have a further serious drawback; they are ineffective at night and under poor light conditions. Targets, picked out by the firer, are lost when he tries to lay an aim. Assuming that the primary task of a Rifle is to hit a point target on the battlefield with an aimed shot, then the optimum design of its sighting system is an essential design requirement. The argument that given a high enough rate of fire, point accuracy does not matter, negates the whole advantage of the Rifle. Experience in counter insurgency operations has shown that targets are usually hard to find, but when they do appear they must be hit first time. Specialist sights do exist that overcome some of the shortcomings already mentioned. The sniper telescope gives a clear aim picture, but must be used by a skilled man and is far too slow and deliberate in operation for general battle shooting. The family of image intensifiers coming into service enable targets to be engaged out to several hundred meters in the dark, but they are heavy, bulky and very expensive. There is a clear need, then, for a general combat sight that will improve the chance of a hit under normal daylight battle conditions and which has a a night capability as well. Conventional sights cannot meet the requirement. Some years ago, this deficiency in small arms sights and recognized by the British Army and a design and development project was placed with the Royal Armament Research and Development
Establishment (RARDE) to produce an improved sighting system. The General Staff Requirements called for a sight with the following main characteristics: 1. Enable the firer to engage targets at night at twice the range at which he can do so with the unaided and desirably at three times the range. 2. Assist Assist in the acquisit acquisition ion and engagement engagement of targets targets with with low background contrast at the effective range appropriate to the weapon. 3. Be capable capable of attachm attachment ent to the follow following ing weapons: weapons: a. Self Self Loa Loadi ding ng Rif Rifle le b. Genera Generall Purpose Purpose Machine Machine Gun (Ligh (Lightt role) c. 5.56 5.56 mm mm M16 M16 Rif Rifle le Anyone who has used a pair of binoculars at night will know what a useful aid such a simple optical device can be in identifying objects. RARDE based their sight on the concept of half a pair of binoculars, fitted with an internal aiming pointer and mounted on the top cover of the Self Loading Rifle. Following comprehensive trials by the British Army the sight is to come into service as the Sight Unit Infantry, Trilux, L2A2, or SUIT. The sight is currently being produced for MOD in production quantities by Avimo Limited of Taunton. The Sight Unit has a prismatic optical system with a magnification of and a field of view of 8 degrees. Any increase on these parameters cause the sight to become too bulky. The eyepiece is located centrally over the Rifle axis for use by both left and right handed firers and the objective lens is offset to clear the foresight and muzzle. The eyepiece is protected by a rubber eyeguard, which helps to position the firer’s eye correctly for a quick shot. The eye relief is only 3 mm and by simply pushing the eyeguard against his brow, the sight is correctly aligned. The system has a fixed focus, so no fine adjustment is necessary. Light transmission is listed as 86%. The aiming mark consists of an inverted pointer with a conical tip that comes down to the centre of the field of view. The tip can be illuminated to a dull orange glow by means of a small tritium (trilux) source that is mounted in the sight body and which needs no external power fully. A brightness control lever enables the degree of illumination to be varied from zero up to maximum. The orange colour selected has been found to produce the minimum loss of night vision.
A correct aim is achieved by simply placing the tip of the pointer onto the centre of the target. The Sight Unit is 71/2in. (18.8cms) long, weighs only 12 oz (340 grams) and is sealed against ingress of moisture. Because of this, the range adjustment is not applied to the pointer, but by moving the whole sight on its mounting. A range lever on the right hand side of the body operates a cam, raising or lowering the rear of the sight. There are two range settings, normally 300 meters for use by riflemen and 500 meters when the sight is fitted to the light machine gun. Zeroing to the individual has been made as simple as possible. There are elevation and direction screws marked E and D (elevate and depress) and L and R (left and right) that can be adjusted by the firer himself with an ordinary screwdriver or even a small coin. The assistance of an armourer is not necessary. Zero is not lost when the sight is removed. The sight is attached to the Self Loading Rifle by means of a spring latch which engages over a claw on the Rifle top cover. Should the sight become unserviceable, the latch can be tripped and the sight lifted clear, enabling the firer to continue using conventional sights. Attachments have been designed that enable the sight to be fitted to a variety of weapons, including the General Purpose Machine Gun, the 5.56 mm M16 Rifle and, more recently, the 84 mm Carl Gustav recoilless anti tank gun. Here a clicker device allows for aim off against moving targets, avoiding the need for a special graticule. A trials programme, lasting many months, has been conducted at the British Army School of Infantry, comparing the new Sight Unit with a number of other sights. The results have been very encouraging. Standard accuracy grouping tests showed that, on average, when using the sight, group sizes were reduced by 3-in at 100 metres. Under low light conditions, the range at which targets could be effectively engaged was at least doubled, even when trialed against conventional sights fitted with an illuminated foresight. The engagement range was found to depend on the amount of ambient light available and the degree of target/background contrast. Against difficult, camouflaged targets by day the sight proved useful as a surveillance and acquisition aid, enabling the firer to pick out targets in close cover. This was particularly helpful when firing the General Purpose Machine Gun at targets out to 600 meters.
Further trials were conducted under normal daylight conditions against conventional iron sights using a variety of moving, short exposure and pop up targets. It was found that firers using the Sight Unit took very slightly longer to bring the target into their field of view, but because their sight picture was clearer and aiming more simple the hit rate at pop up targets was comparable and in the case of moving targets, better. Firers considered that there would be very few occasions, if any, when they would prefer to use their conventional sights. The only conditions that succeeded in defeating the sight were thick mist or driving rain, a problem with all magnifying devices. External misting of the optics themselves was not the problem that had been feared. It never prevented the use of the sight and a quick rub with a handkerchief or even a beret quickly cleared it. Robustness is an essential requirement in any military equipment and in addition to the usual shock tests, temperature cycling, etc, the sight was given more down to earth treatment during the trial, including many drops onto a barrack room floor and frequent trips over the assault course. At the end of them the sight was still fully operational. Based on the results of the School of Infantry trials it seems that RARDE has produced a sight that fully meets the General Staff Requirement and that is proving to be an effective general purpose combat sight for small arms, superior in nearly every respect to the conventional iron sights that have been in service for so many years. It provides a night fighting capability, albeit at a reduced range, at a fraction of the cost of an image intensified sight. The fact that one interchangeable sight will fit 3 of the standard weapons in the infantry platoon gives a further payoff in flexibility and economy. The British Army is currently putting much effort into improving its standard of battle shooting; the Sight Unit Infantry, Trilux will be an important factor in achieving that aim.
Nomenclature: Sight Unit Infantry Trilux L2A2 NSN: 1240-99-964-7647 Dimensions: Length: 18.8 cm Width: 7.6 cm Height: 6.9 cm Weight: 340 gm Reticule: Illuminated inverted post. Range Settings: 300m (rear), 500m (forward) Magnification: 4X Objective Aperture: 25.5 mm Field of View: 8 degrees (140 mils) Light Transmission: 86% Exit Pupil Diameter: 6.6 mm Eye Relief: 35 mm Environment: -75deg to +90deg Active Element: 0.22 curies of Tritium gas Illumination color: Red Manufacturer: Avimo Ltd. MANUAL
Ministry Mini stry of Defence Defenc e
S.U.I.T. S.U.I .T.
User Handbook For
SIGHTUNIT INFANTRY TRILUX NSN 1240-99-964-7647 RESTRICTED
SIGHTUNIT, INFANTRY, TRILUX OPERATOR’S MANUAL
The Sightunit, Infantry, Trilux L2A2 (Fig 1). A detachable optical sight with a magnification of four, equipped with an internally illuminated inverted aiming pointer. With the sight fitted the Infantryman’s night vision capability is extended enabling him to engage targets at longer distanced. The amount of improvement depends on the light falling on the target and the target/background contrast. The increase in range varies from two to three times that of conventional open sights. By day, the sightunit assists in the acquisition and engagement of targets with low background contrast at the effective range of the weapon to which it is attached. IT also forms a useful surveillance aid. A range control lever provides settings for 300 and 500m. The sight is zeroed by alteration to the elevating and lateral adjustment screws. A Pouch, Sightunit, Infantry L1A1 is provided (Fig 2).
Body (Fig 3). The aluminum body is of monocular construction and contains the optical system. It is provided with a cover secured by socket head screws. The eyepiece, placed centrally, enables the sight to be used by right or left handed firers. The objective lens is offset to the left to avoid the iron foresight or rifle muzzle interfering with the field of view. Incorporated in the optical system is an erecting prism and telephoto lens.
RESTRICTED An inverted clear plastic pointer with roughened conical tip forms the reticle and is located within a holder in the top of the body. Viewed in daylight, the reticle appears as a darkened pointer containing a clear narrow vertical line. A lamp holder held in position by a circlip and containing an orange/red Trilux lamp, is provided with a knob which enables the operator to vary the degree of illumination from zero to maximum. By rotating the knob the lamp can be either offset, or moved directly over the reticle where the light is reflected down the clear plastic tip and the tip illuminated. Attached to the eyepiece is a rubber eyeguard which is secured by an adhesive. (See Trilux Lighting Safety.)
[NOTE: Aiming pointer is inverted.] The Arm (Fig 3). Fixed to the underside of the sight body the arm is designed to secure and align the sight correctly to the rifle. A latch, mounted on top of the arm and pivoted on a spring clip, facilitates the attachment and removal of the sight. A continuous spring clip, hooked to each side of the latch, passes under the arm and secures the sight to the central attachment point of the mount. Upward rotation of the latch causes the short arm to force the spring clip down and clear of the central attachment point on the mount. A pin, with cams located each end and held in a recess towards the rear, is attached to the range control lever. With the range control lever in the vertical position the sight is set for 300m and 500m is obtained by pushing the lever fully forward. A stop on the right side of the body and the flange to which the rear cover is secured, assist in retaining the lever in position when the sight is detached from the weapon.
RESTRICTED An internally threaded alignment block, with curved recess to receive the mount locating pin, is attached to a lateral adjustment screw. An inscribed guide R L located above the lateral adjustment screw, indicated the direction of rotation required to move the MPI right or left. Eight graduations each corresponding to an alteration of 100mm (4in) at 100m, are engraved on the arm close to the screw head. [NOTE: If your SUIT is missing the sticker or it’s an Israeli model in Hebrew, for windage adjustments counter-clockwise is right and clockwise is left.]
An elevating adjustment screw with conical point for location in the forward cradle of the mount is situated at the front end of the arm. A guide marked E D (elevate and depress), indicated the direction of rotation required to correct any vertical errors. The eight inscribed graduations each indicate an alteration of 100m (4in) at 100m. Located in a horizontal boring and placed one either side of the elevating screw, two cones, one with an internal thread, are retained in position by an elevating clamp screw. Clockwise rotation of the elevating screw causes the cones to bear against the forward edge of the elevating screw and retain it in
position. Tightness of the elevation clamp screw must be checked periodically. RESTRICTED
The Mount (Fig 4). The mount consists of a rifle top cover and adapter. A locating pin fixed towards the rear of the mount bears against the curved recess of the alignment block. Slightly to the rear of the locating pin is a platform on which the range cam control operated. A V-notched cradle at the front of the mount provides a seating for the elevating screw. Positioned approximately mid-way between the locating pin and the cradle is a central attachment point for the sight spring clip. [NOTE: The original mount is notorious for the rivets working loose under prolonged recoil. Someone with a TiG welder can fix it permanently.]
Fitting the Sight (Fig 5). Remove the sight from its pouch and raise the latch fully. Position the sight over the mount and locate the conical point of the elevating screw in the V-notch of the cradle. Lower the sight on to the mount so that the locating pin engages the recess in the alignment block. Push the latch fully forward and test the sight for security. An alternative method of fitting is to position the locating pin in the recess of the alignment block first, then lower the front until the elevating screw fits into the cradle. Removing the Sight. Raise the latch fully, check to see if the spring is disengaged from the attachment point, lift the sight off. If the spring is not disengaged ease the sight up and forward carefully. Failure to take care may cause damage to the rear lugs on the sight and to the spring. RESTRICTED
Using the Sight by Day. Adjust the range control lever as required. Use the 300m position for targets up to 400m. Push the range control lever to the 500m position for targets between 400 – 600m. Using the Sight by Night. Set the range control lever to 300m. Adjust the brightness of the reticle by rotating the brightness control knob. Care and Maintenance. The sight is a sealed instrument and must never be opened by other than qualified personnel. The sight should be inspected at frequent intervals and the body wiped over with a dry cloth. Careless cleaning of the lenses may lead to scratches. Particles of dust and grit must therefore be blown clear before the lenses are wiped over with a clean tissue or lint free cloth. Lenses must not be rubbed violently. The cleaning can be assisted by breathing on the lenses. Spots or stains may require the use of methylated spirits on a piece of clean sloth.
SAFETY Trilux lamps have no significant level of external radiation and no hazard can arise unless a lamp is broken. Breakage of the lamp and the release of tritium gas can result only from misuse of the equipment. In the event of breakage, the following precautions should be taken. a. The escaping gas should not be inhaled. b. The broken parts should not be handled with bare hands. c. If breakage occurs indoors, doors and windows should be opened to allow gas to clear. There is little danger if breakage occurs outdoors. d. Any breakage must be reported immediately.
The TAPCO “T-Bar” adapter allows you to mount a SUIT on a conventional Weaver/Picatinny top cover scope mount.
15-Meter bore-sight target
