History

"Backbone" has been the subject of careful research, much speculation and what might be considered as conspiracy theories. For an example of the former I recommend the Subterranea Britannica article Backbone Microwave Relay Network written by Steve Fox and Richard Lamont. Using primary sources this documents the progress from an initial concept in the mid-1950s to the subequent selection and development of sites (many of which were different from the original plan). This research concludes: "It seems that the original Backbone stations became absorbed into a much larger microwave network..." Fox and Lamont also comment that there was little or no mention in archive files relating to defence communications in the 1960s.

Subsequent research in BT Archives and an Audit Office file relating to contracts for development of the UK Inland Microwave network has uncovered more detail of the development of Backbone as a "network within a network". Changes to the bigger picture, notably defence radar, meant that many of the strategic sites identified in the 1950s plans were no longer of significance.

The following pages document the individual sections of Backbone, with contract and other details.

Jumping forward to the 1980s, documents relating to "government" functions retained by British Telecom disclose the continued operation of a separate Backbone SHF network, designed primarily to support the Emergency Manual Switching System. An "All Underground" cable network had also been developed to provide resilient links for EMSS. The structure of EMSS is a close match for some parts of Backbone - for example Lancaster, York and Peterborough were all top-tier nodes in EMSS and are served by Backbone Branches. The documentation also reveals the way in which Backbone was cross-connected to "All Underground" and to other cables. The EMSS node at Lancaster was connected via cable to the Backbone site at Quernmore, and the tier-two node at Darlington was connected via its own spur from Backbone.

It is no longer a secret that Five Ways served the Central Government War Headquarters (CGWHQ) at Corsham - but it was less obvious that the CGWHQ was also connected via a cable from the next tower at Wotton-under-Edge. The northern extremity at Craigowl was connected to Dundee by cable and thence to the top-tier EMSS node at Perth. The south eastern end of Backbone at Fairseat is likely to have connected with cables from the London area and most likely continued to a connection with the "All Underground" network towards the EMSS node at Reading. Backbone was therefore not a stand-alone system intended to survive under all conditions but part of interconnected networks providing resilience through diversity. The sixth top-tier EMSS node at Worcester was on a trunk cables running from Cheltenham to Shrewsbury. Cheltenham was connected to CGWHQ via cable, with another cable link running from Shrewsbury to the Backbone site at Albrighton.

A frequent misunderstanding has been the role of the concrete towers within the Post Office SHF network - one widely held theory is these are blast proof and specifically Backbone sites. In practice Backbone was required to avoid built-up areas which might have been targetted and therefore bypasses the concrete towers at Manchester (Heaton Park) and Leeds (Tinshill). Some of the "important" sites within Backbone were steel towers: Hunters Stones and Copt Oak. Another myth was the capacity. EMSS was intended to protect essential communications only and Backbone provided a maximum of 600 circuits over the main section, with some branches restricted to 240 circuits.

Documents from the 1980s show there were concerns about the condition of the Backbone equipment and a failure in a "no break" power supply had led to a lower level of protection at one site (unnamed). BT was pressing for approval to transfer traffic to other links or for plans to be made for replacement equipment. The outcome was to close Backbone by the end of 1989. EMSS and the "All Underground" network closed by February 1993 - users having transferred to alternative systems.

Although Backbone traffic was segregated the vast majority of sites were shared with general telephony traffic. Two notable exceptions were Muggleswick, which provided a means for Backbone to avoid the Newcastle area, and Pimlico (Hemel Hempstead) which was used to create a link avoiding central London. Despite their apparent strategic importance, both were provided with cable-stayed masts rather than self-supporting towers. Pimilico was also used for the London Radiophone service and as a television relay - but did not carry any other SHF traffic. All sites were provided with the standard form of building - a single-storey steel-frame with brick walls and flat concrete roof.