Elliott 920M Computer

In 1967 Elliotts had been awarded a major contract for the design, development and integration of a Navigation and Weapon Aiming Sub-System (NAVWASS) for the RAF's new Jaguar aircraft.

The Jaguar was designed as a close air support aircraft for supporting ground troops in daylight. The NAVWASS enabled the pilot to navigate and fly at low level and high speed to acquire and accurately attack targets. Trials of the prototype Jaguar system were carried out using a Varsity aircraft at West Malling airfield in Kent

The Jaguar NAV/WASS  sub-system comprises four principle groups of equipment. The sensors, which measure what the aircraft is doing and feed these measurements into the computer; the computer sub-system which processes this measured information into a form which can be used by the pilot; the cockpit controls which control the system's mode of operation and lastly, the cockpit displays which show to the pilot the computer's outputs of converted measurement information and also information, such as target or waypoint position, which is being input into the computer. The system included an E3R inertial platform, Digital Computer, a HUD, Projected Map Display, Horizontal Situation Indicator and various cockpit control panels.

The 920 series of computers was developed at Elliotts Borehamwood Computing Division in the 1960’s and was derived from the successful 901 commercial computer which was miniaturised for airborne use. One of the primary production derivatives was the MCS 920M which was used in the
Jaguar Navigation and Weapon Aiming Sub-System NAVWASS This system comprised the MCS920M central digital computer, E3R inertial platform, projected map display and horizontal situation indicator together with the necessary power supply, electronic, interface and control units.
The MCS 920M is a microminiature general purpose digital computer using flat pack integrated circuits and. has a random access, 8192 word, 18 bit ferrite core store with a 2microsecond cycle time. Elliotts lacked access to multi-layer printed circuit board technology so used a special technique developed at the Borehamwood Computer Laboratory (see ‘Moving Targets’ by Simon Lavington). The box is unusual in that it folds out into three blocks.
In addition to performing navigation and weapon aiming calculators, the computer caters for in-flight monitoring, initial alignment and in situ first line system testing. The Computer also had an Interface Unit which enables the digital computer to receive and transmit information from and to other units in the aircraft in compatible signal form. The Interface Unit also supplied the power for the computer and Navigation Control Unit.
In its production form the MCS920M was widely used in its intended role in the Jaguar navigation attack system and eventually grew to a 64 K machine. The 920M also saw use in the ELDO rockets.
The MCS920M was also adopted for a number of naval inertial navigation applications.