the rear. The six-wheel chassis was based on then standard British Railways practice, albeit it with specially made and shaped side frames and bespoke tank and bodywork assembled at Vulcan Foundry. The locomotive had a designed maximum speed of , weighed , and was painted in a lined Beech Leaf Brown Livery, earning it the nickname "The Chocolate Zephyr" amongst railway enthusiasts. Underframes, grilles and the front access and cab doors were painted Brunswick Green with lettering and lining in Orange. Testing The locomotive was taken to British Railways' Rugby test centre in an incomplete state for testing on rollers, and then on a short section of specially laid track. After returning to Vulcan Foundry for final assembly, the locomotive was then based at the former locomotive shed at Whitchurch in Shropshire for initial light testing and crew training on the Malpas Line, before commencing loaded test runs to Llandudno. One of these runs was filmed from on board the locomotive by British Movietone News and the resulting film also shows the locomotive being turned on Llandudno Junction turntable. In the event not all of the planned North Wales Coast Line test runs were completed. GT3 then moved to Leicester Shed on the former Great Central Main Line line for testing and crew training between Leicester and Woodford Halse and then Leicester and Marylebone. Leicester was convenient for English Electric's Whetstone turbine works. During this period it was displayed at Marylebone for the 50th anniversary of the Institute of Locomotive Engineers. The event ran from 11 to 14 May 1961 and GT3 was filmed by British Pathé being inspected by the Duke of Edinburgh. Later testing was undertaken on the West Coast Main Line from Crewe over Shap summit. On one of these runs O S Nock travelled on board and was able to both witness the locomotive in operation and record its performance, his log of the trip later appearing in Railway Magazine's practice and performance feature for February 1962. Commenting on the testing the designer noted that, despite some of the expected teething troubles and modifications, once it had departed on a test run GT3 had never failed to complete its booked workings. The locomotive was described as being comfortable and easy to handle for the crew, with conversation at normal volumes possible in the fully enclosed cab. Demise Despite returning favourable performances on longer runs requiring sustained