The original Rapier took the form of a wheeled launcher with four missiles, an optical tracker unit, a generator and trailer of stores. The launcher consists of a large cylindrical unit carrying two missiles on each side, the surveillance radar dish and "Identification friend or foe" (IFF) system under a radome on top, the guidance computer and radar electronics at the bottom, and a prominent parabolic antenna for sending guidance commands to the missiles on the front.
The search radar was of the pulsed Doppler type with a range of about 15 km. The aerial, located at the top of the launcher, rotated about once a second, looking for moving targets that are "visible" due to their doppler shift. When one was located, a lamp would light up on the Selector Engagement Zone (SEZ), a box containing 32 orange lamps arranged in a circle about the size of an automobile steering wheel. The radar operator could also blank out returns from other directions, providing jamming resistance.
The optical tracker unit was made up of a stationary lower section and a rotating upper section. The lower section housed the operator controls, while the upper section housed the tracking optics. The operator's optical system was a modified telescope containing a Dove prism to prevent the image 'toppling' as the optics rotate in azimuth. This system meant that, unlike a periscope, the operator did not have to move in order to track the target. The upper section also contained a separate missile tracking system that was slaved to the operator's optics, based on a television camera optimized for the IR band.
Upon detection, the optical tracking system would then be slewed to target azimuth and the operator would then search for the target in elevation. The operator's field of view would depend on the target range: "wide" at about 20 degrees or "track" at about 4.8 degrees. When the target was found the operator switches to "track" and uses a joystick to keep the target centred in the telescope. Once a steady track was established the missile was fired. The TV camera on the tracker was tuned to track the four flares on the missile's tail. Like the operator's telescope, the TV system had two views, one about 11 degrees wide for the initial "capture", and another at 0.55 degrees for midcourse tracking.
The difference between the line-of-sight of the operator's telescope and the missile's flare was calculated by the computer in the base of the launcher. Guidance updates were sent to the missile through the transmitter on the launcher platform, and received on small antennas on the rear of the mid-body fins. The operator simply kept the telescope's crosshairs on the target using the joystick, and the missile would automatically fly into the line-of-sight, a system of operation known as SACLOS. The basic concept is very similar to the one used by most anti-tank missiles, with the exception that those systems normally use small wires to send guidance information to the missile, rather than a radio link.
The missile contained a small 1.4 kg warhead with a contact fuse and a single-stage solid-rocket motor that accelerated the missile to about 650 m/s. Engagement time to the maximum effective range was about 13 seconds. Response time from the start of the target detection to missile launch is about 6 seconds, which has been repeatedly confirmed in live firing.
The whole system, along with its crew, was delivered by two Land Rovers designated as the Fire Unit Truck (FUT) and the Detachment Support Vehicle (DSV). Royal Artillery batteries comprised three troops each of four fire units while RAF Regiment squadrons had eight fire units. By 1980 each Royal Artillery fire unit consisted of a (24 volt) 101 FC 1 tonne Land Rover towing the Rapier Launcher and carrying 4 missiles on board, a 109-inch 3/4 ton 24v FFR (Fitted For Radio) Land Rover towing a 1-ton Missile Supply Trailer (MST), containing up to a further 10 missiles. Blindfire radar (see below) was only provided for 1/3 of fire units in British Army service, and for all fire units in the RAF Regiment.