The Deltic (or Class 55) was one of the most powerful diesel locomotives ever to run on the British Railways network. Capable of a top speed of 100mph, its 'maintenance by replacement' system at Doncaster Works meant it set expectional standards for reliability and availability. From the 1950s until the start of the 1980s, the Deltics saw service between London and Aberdeen on the East Coast Main Line's Deltic fleet - once the most powerful locomotives in Britain. The Deltics had revolutionised rail travel in the late 1950s. Only 22 were ever built but over 10 survive in preservation today and some have even been hired out for main-line service in the past three years. The 'Deltic' captured the imagination of the public and represented the peak of the diesel era. Alastair McLean, a railway enthusiast and author, memorably photographed the last season of running in 1981 in black and white.