Ferranti Argus 500 computers were added to this as the Recognised Air Picture Dissemination System (RAPIDS) which also extended the RAP to 1900 by 1900 nautical miles. Long-range early warning data was also fed through data links to and from NATO and French radar sites. Other parts of the system were never commissioned, including three more computers that would have integrated the processing of filed civilian flight plans, and data links that would have been used to integrate the Bloodhound missile's computer systems as well as a link to Fylingdales. The RDPS was working operationally until 1984 when it was scrapped. But the Ahead plan and the Linesman system were one of the earliest visions of using computers for distributive processing in both local and wide area networks. There were even early concepts of packet switching and routing of data. Sites The concept of two main data processing hubs, the L1 and L2, also divided the UK into two areas: the Northern Track Production Area (NTPA) and the Southern Track Production Area (STPA). The L1 primarily looked after the STPA with inputs from four main sites – RAF Neatishead in Norfolk, RAF Staxton Wold in Yorkshire, RAF Boulmer in Northumberland and RAF Bishops Court in Northern Ireland. To this there were also inputs from six civilian radars at Ash, Ventnor, Clee Hill, Burington, London 1 and London 2. It was understood from the start that the L1 site, above ground and made largely of glass, was subject to air attack; as the second "L2" site originally planned to be built underground at Prestwick was never carried out, elements of the air defence system were devolved out to use the standby capabilities of the radar sites, namely the Standby Local Early Warning and Control (SLEWC) systems at RAF Neatishead and RAF Boulmer. Because the L2 was never implemented, the L1 had to extend its processing to cover the Northern Area as well but, with no computer data links, inputs for RAF Saxa Vord, RAF Benbecula and RAF Buchan had to be voice-told for manual input into the L1 system. Later the L1 also took an input from RAF Portreath in Cornwall. Data from Shackleton AEW aircraft also had to be voice-told into the L1 computer system. On the output side, the Recognised Air Picture as the General Situation Display (GSD) was fed out as the Higher Formation Display (HFD) to RAF