History

Disclaimer: I don't have sufficient knowledge of the radar and computer systems used within Linesman/Mediator to provide any detail of the overall operation. For now this account is focused on the microwave links between the radar sites and control. The "Mediator" element of the system used sites operated by what became the Civil Aviation Authority - the CAA set up its own links (these will be documented separately). The "Linesman" sites were operated by the RAF with links provided by the Post Office.

To aid readability only the main links are shown in the map above. Linesman used three radar sites on the east coast: Boulmer, Staxton Wold and Neatishead, each of which needed a link to the central control. Included within the design was a "passive detection" (PD) system which used the adjacent sites to track aircraft which were attempting to jam the main radar frequencies. The PD element required direct links between adjacent sites to access and control a "High Speed Aerial" (HSA). Staxton Wold was able to use the HSAs at Boulmer and Neatishead; Boulmer had access to Staxton Wold and to a stand-alone HSA at Dundonald. Netishead used the HSA at Staxton Wold.

The Linesman links generally operated at 2 GHz over dedicated systems although the sites were shared with other traffic where possible. It is not known whether traffic from Boulmer to London bypassed Staxton Wold or followed an "in and out" routing, however the overall design allowed for independent channels from each main site. A local link was also provided between Staxton Wold and Patrington.

A further main radar at Bishops Court was included in Linesman however it was not equipped with PD facilities and its link to London was carried over the general-purpose route via Belfast, Carlisle, Manchester and Birmingham.

The radar project was ambitious and technically complex. Due to the planned timing, several of the Post Office sites required "urgent" work to provide new towers or buildings before links could be installed. The Air Ministry's priorities appear to have been the link between Boulmer and Staxton Wold and Boulmer to London, with some temporary arrangements being provided.

The following pages document the individual Linesman links, with contract and other details.

• Staxton Wold - Patrington
• Dundonald - Boulmer
• Boulmer - Staxton Wold
• Staxton Wold - Neatishead
• Boulmer - London
• Staxton Wold - London
• Neatishead - London
• Bishops Court - London

A file at BT Archives (Finding Number TCB 711/7/4) "Setbacks and Delays in completing radio-relay links required for 'Linesman' Scheme" documents progress (or otherwise) between January 1966 and late 1967. In a letter to Air Vice Marshall Porter, the Post Office Deputy Engineer-in-Chief (J.H.H. Merriman) noted the handover of the Boulmer - Staxton Wold link "tomorrow" (15 January 1966). However Merriman explained "we are at the mercy of one contractor for all the fabricated steel-work for our towers". The letter also includes the comment "I have discovered that the system we are providing is being engineered to particularly close transmission delay tolerances. [...these] make it impracticable for you to benefit from the more normal re-routing or other emergency restoration services that we would put into operation under break-down conditions."

On 31 March 1966, Air Commodore Powell wrote to Merriman: "It is nevertheless most disturbing and of the greatest possible concern to those concerned with the progressing of the Linesman/Mediator project to learn of still further substantial slippages...". Powell noted the latest dates for Neatishead - Staxton Wold (December 1966), Neatishead - West Drayton and Staxton Wold - West Drayton (both May 1967) and further commented:

"The Linesman/Mediator project is one of the most important and certainly most expensive defence radar projects ever undertaken in the United Kingdom...The successful completion of the Linesman (Stage I) portion by the "O" date October 1968 is utterly dependent on the timely provision of the necessary radio links. As a result of the slippage [of Neatishead - Staxton Wold] which is the Passive Detection link, we face the complete rescheduling of all PD flight trials. Without the other two links, which connect radars with the Master Control Centre, there can be no proving of the sub-systems within the latter."

The file includes papers relating to a meeting between PO and MOD in April 1966. Pencil notes suggest discussion of the dates when the towers required for Neatishead - London would be available: late 1966, with service commencing mid-1967. A subsequent letter from Powell to Merriman gave the dates agreed at the April meeting and those reported in October 1966.

A note dated 12.9.66 gives further explanation for some of the delay. The link between Dundonald and Boulmer was subject to completion of the new building and tower at Wooler and to acquisition of a new site at Craiglockhart ("possible RFS of link 6/68") however it seems an interim solution would be provided by March 1967. Most of the other links were noted as being subject to delays with towers, however Boulmer - Staxton Wold was reported as operational yet requiring equipment modifications. Staxton Wold - Patrington was subject to a planning application for a new site at Hornsea and the link for Bishops Court (referred to as Killard Point) was expected by November 1968.

It appears that once the towers were completed there were issues with the radio links. A Confidential note dated December 1966 shows GEC were having to modify their equipment since: "... G.E.C. had failed to appreciate a particular Clause in specification calling for certain linearity requirements and the equipment as produced had failed to meet these. [...] the solution to the problem had been found and the equipment was in the process of being modified to bring it up to standard. However this involved certain supply difficulties and the equipment would not be available from the factory before April, 1967". It was further reported: "Air Commodore Powell said that the M.O.D. could not accept these delays and he thought a firm of the size of G.E.C. should be able to make some special arrangement to meet the dates required. [...] he hoped that the matter would not have to go to Ministers".

On 27 January 1967 the Assistant Engineer-in-Chief (H. Stanesby) write to Air Commodore Powell. After discussion with GEC it had been agreed to offer completion of the three routes to London by mid-July 1967, however "on a part-time basis and without normal protection, in order that the commissioning of associated Ministry of Defence equipment might proceed. Acceptance testing [by the Post Office] will be carried out simultaneously on the channels not being used by M.o.D." This letter concluded: "I should emphasise there is virtually no slack in the present program and that any unforeseen difficulties arsing could still give rise to further delay. However, G.E.C. and we ourselves will continue to do everything possible to ensure that links are available in adequate time to meet the full-time service date for the scheme as a whole, of December 1967.

Powell replied to Stanesby on 1 February, requesting "...the date on which we could expect from you fully protected links in their final form". The response from the Post Office was delayed until 3 April. A draft dated 27 March includes a comment that the connection between the Post Office Tower and West Drayton - a cable provided by STC - had been programmed to be made availale to meet the (delayed) dates for the radio links. As a consequence it would not be possible to provide full service over the cable section when the interim radio links became available! The final version of the letter omits this detail but offered a partial service: two cables would be available initially and would be switched between the three radio links as required. Again Stanesby commented that PO testing would be carried out in parallel with the MOD's initial use of the links, however it was expected the whole system would be completed by 1 November 1967.

According to a booklet produced in 2008 to mark the closure of the air traffic control centre at West Drayton: "By 1970 the equipment had been installed and programming was under way. However the project quickly ran into serious technical problems...[...] Eventually the system was handed over to the RAF in 1974. By that time the computers were obsolete, the development of computer languages had advanced and the threat had altered." Astonishinly, the booklet then states: "Eventually, in 1978 Linesman was decommissioned and sold for scrap". This closure date does not match with the continued operation of the link from Bishops Court to London until the mid-1980s, however that may have been for other purposes as Bishops Court also served as a civil radar.

The 1960s links were wide-band and (as mentioned above) required delay to be within tight tolerance. However by the late 1970s the technique of "plot extraction" had been refined to the point where radar data could be passed via a standard telephone line. It seems likely the dedicated Linesman links from the east coast sites would have been withdrawn from service in the early 1980s.

Details of each route are given on separate pages, however the overall network required very few sites which were either already in operation or had been planned for general purpose use. The main exceptions were the six radar-related sites: (Boulmer, Staxton Wold, Neatishead, Bishops Court, Patrington and Dundonald (HSA) - the buildings at these sites appear to have been the responsibility of the MOD and in general stayed masts were used to carry the antennas. Greenfield Hill was required as an intermediate site between Dundonald and Kirk o'Shotts, also receiving a stayed mast but a standard Post Office building. Claxby appears to have been added to reduce the number of "hops" required on the link between Staxton Wold and London. Other sites were re-used from early television links or those which would be developed as part of the London - Leeds and Leeds - Hull telephony routes.