prototype locomotives came in the use of axle-hung, rather than frame mounted traction motors; this feature would later prove very problematic for the class. The order for 100 locomotives was placed in 1963; it was split between two manufacturers, with the English Electric Vulcan Foundry in Newton-le-Willows building 60 locomotives and British Rail Doncaster Works producing 40. The Doncaster and Newton-built locomotives were not identical; the Newton-built versions had a power output of , whilst the Doncaster-built examples were rated at , due to a different design of traction motor. British Rail service The class was introduced officially into service in August 1965; the entire fleet was delivered within 24 months of that date. In the early years, the locomotives became notorious for rough riding, and causing track damage, being fitted with axle-hung traction motors in place of the bogie-frame-mounted motors of the earlier designs; this additional unsprung mass was causing damage at speeds in excess of . In 1969, E3173 was fitted experimentally with the large helical 'flexicoil' springs. Trials carried out under the direction of the British Rail Research Division proved successful and the modification was applied gradually in phases to the whole fleet. As a result, the first batch of Class 86s were modified with improved suspension and, from 1971 onwards, locomotives were renumbered progressively into two subclasses; 86/0 (numbers 86001–86048), which remained in as-built condition, and had their maximum speed reduced from to and which were generally restricted to use on freight and slower passenger services, and subclass 86/2 (86204–86252), which were fitted with the improved suspension and retained the 100 mph maximum speed. Within a short time, a further batch was modified to the new specification and renumbered accordingly; 86040–86048 became 86253–86261. In 1970, locomotive E3173 was also fitted experimentally with a streamlined nose cone made from fibreglass; this was to assist BR's research into aerodynamics and high-speed running for their new Advanced Passenger Train and High Speed Train, which were under development. The locomotive was tested on the WCML in the area; it reportedly reached speeds of , which made it the first BR locomotive to beat Mallard's speed record. The record was not publicised however, as BR did not want the event to overshadow their new trains. At the same time, three Class 86s were converted into test-bed locomotives for development of the Class 87; they were numbered initially to 86201–86203, refitted with