Appendix Two

THE ROTOR PLAN AND LINESMAN/MEDIATOR

The ROTOR Plan

At the end of WW2, there was a sprawling network of some 170 radar sites employing a mixture of metric and centimetric types, many being left-overs from the Chain-Home and Chain-Home-Low radars which played a crucial role in the Battle of Britain and thereafter throughout the rest of the war.

The perceived post war threat from the USSR, led the UK Government to issue, in 1949, the ‘Cherry Report’, which recommended an urgent review, overhaul and improvement of the UK`s air defences under the code name ‘ROTOR’ aimed at reducing the original 170 sites to 66 and bringing the performance of each remaining site up to the best available peacetime standard. This was a major task and was divided into two stages. The lead company chosen by the government to oversee the ROTOR STAGE 1 programme was the Marconi Wireless and Telegraph Company. The Decca Radar Company (as it was at that time) was invited by the Government to participate in this programme by the provision of a new long range primary radar based on the RRE Green Garlic concept. Decca Radar was charged with the task of designing, manufacturing and commissioning the electronic sub-systems of this radar, which was designated Type 80.

As has been explained earlier, the first production model was installed at RAF Trimmingham on the Norfolk coast and handed over to the RAF in 1954. Others followed and by October 1955 four Mark 1’s Type 80s had been handed over to the RAF.

Exceptionally high winds swept the north of Scotland in January 1956, and the Type 80 equipment at Saxa Vord was damaged, the antenna became badly strained. As a result, the centre section of the antenna framework had to be strengthened on all models. This, together with other problems introduced a delay in the production and commissioning programme of the Mark 1 equipments. The up grading of Mark 1’s to Mark 3 also suffered delays due to production problems at The English Electric Valve Company, with the newly developed 2.5 Mw magnetron. Additionally, there were some cancellations of Mark 3 orders, such that by 1957 the total number of operational Type Mark 3’s had reduced to 15. This was some 5 or 6 less than the number originally planned to be operational by that date.

As there were a number of other radars of various types produced and installed by other British manufacturers, the total radar UK capability in 1958 was judged by MOD to justify the declaration that the ROTOR STAGE 1 milestone had been achieved.

A new ROTOR programme (STAGE 2) was initiated resulting in the total number of Type 80s installed on UK RAF stations in 1960 reaching 22. These were at the following locations: -

Anstruther Bawdsey Holmpton Hope Cove Neatishead St.Annes
Sandwich St.Twynells Scarnish Patrington Tiree Seaton Snook
Aird Uig Skendleby Sopley Treleaver Saxa Vord Wartling
Killard Point Buchan Trimingham

Many RAF stations were also fitted with HF200s, some with two height finders on each site.

The installation of the Type 80 antennas on top of the turning gear was carried out in three stages. Each antenna was supplied as three 25 feet wide sections. A crane lifted the central section onto the turning gear followed by the lifting and attachment of the outer sections. This was a delicate operation and required that the wind force did not exceed 10mph. At Benbecula, in the Shetlands, the wind never dropped to that level, so the installation of a Type 80 was abandoned.

LINESMAN/MEDIATOR

Linesman/Mediator was dual-purpose civil and military radar network, replacing the earlier ROTOR and Type 80 MASTER Radar Stations. LINESMAN, with a small network of five large radar sites and an associated control centre near London, was the air defence element of the project. MEDIATOR was the civilian air traffic control element. LINESMAN was modified over the years until replaced by the Integrated United Kingdom Air Defence Ground Environment System (IUKADGE).

The concept was to reduce the complexity of the existing distributed ROTOR system by using multiple ‘MASTER’ Radar Stations in conjunction with a single control centre providing a complete air picture of the UK. This, together with inter-site communication up-grades, enabled Command & Control of military aircraft to be effected on a national scale. In addition, measures were initiated to improve the resistance to jamming. The existing Type 80, although very powerful, was relatively easy to jam.

To augment the existing Type 80, a new Type 84 radar was to be included. The improved LINESMAN plan proposed that three new radars should be developed, two primary long-range search radars; Marconi`s Type 84 and the AEI Type 85 (Blue Yeoman), with additional height finding capability provided by the Decca HF200 (the Type 85 being multi-beamed in elevation had a height determining capability). To improve system resilience to jamming, the two primary radars operated on different frequency bands, the Type 84 in L-band, the Type 85 in S- band.

The Type 85 included an advanced ECCM system using frequency diversity. The radar had 12 transmitters, the final stages using klystrons. Each transmitter had a peak power output of some 5Mw, thus giving 60 Mw total peak power output.

During various reviews of LINESMAN it was decided to incorporate civilian air traffic control (the MEDIATOR system). The combined LINESMAN and MEDIATOR systems were ultimately housed in a new building at West Drayton, with the Marconi Company providing the displays and Plessey Radar the signal-processing element.

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