and the Eastern Region declined to accept further machines as they deemed them unsuitable to replace the Pacific steam locomotives on the East Coast Main Line, preferring to hold on until the "Deltic" Class 55 diesels were delivered. The London Midland Region was only too pleased, as the Eastern Region's decision released additional locomotives to replace their ageing steam fleet. The West Coast Main Line had been starved of investment for many years and the poor track and generally lower speeds (when compared to the East Coast route) suited Class 40s, as the need to hold trains at speed for long periods simply did not exist and it better took advantage of their fairly rapid acceleration. Production Following the mixed success of the prototypes, another 190 locomotives were ordered by British Railways, and were numbered from D210 to D399. All were built at Vulcan Foundry, except one batch of twenty (Nos. D305–D324) which were built at Robert Stephenson and Hawthorns factory in Darlington. All the locomotives were painted in the British Railways diesel green livery, and the final locomotive, D399, was delivered in September 1962. Batches of the class were built with significant design differences, due to changes in railway working practices. The first 125 locomotives, Nos. D200–D324, were built with steam-age 'disc' headcode markers, which were used to identify services. Later, it was decided that locomotives should display the four character train reporting number (or headcode) of the service they were hauling, and Nos. D325–D344 were built with 'split' headcode boxes, which displayed two characters either side of the locomotive's central gangway doors. Another policy decision led to the discontinuing of the gangway doors (which enabled train crew to move between two or three locomotives in multiple). The remaining locomotives, Nos. D345–D399, carried a central four-character headcode box. In 1965, seven of the first batch of locomotives, Nos. D260–D266, which were based in Scotland, were converted to the central headcode design. From 1973, locomotives were renumbered to suit the TOPS computer operating system, and became known as 'Class 40'. Locomotives D201 to D399 were renumbered in sequence into the range 40 001 to 40 199. The first built locomotive, D200, was renumbered 40 122, which was vacant due to the scrapping of D322 as the result of accident damage. The named 40s Locomotives in the range D210–D235 were to be named after ships operated by the companies Cunard Line,