Gresley was to unveil his design first, the A4 class 4-6-2 pacific locomotives, which entered service hauling the Silver Jubilee train from London King’s Cross to Newcastle. During its inaugural journey, on 27th September 1935, A4 class locomotive 2509 Silver Link set a new speed record of 112 mph. The train was a commercial success and the LNER introduced more services hauled by streamlined locomotives over the next few years.
Not to be outdone, Napier decided to add streamlining to his new design, the Princess Coronation class 4-6-2 pacific locomotives. On 29th June 1937, locomotive 6220 Coronation pulled a special LMS train from London Euston to Crewe carrying newspaper reporters in order to gain as much publicity as possible for their new Coronation Scot service. The driver T. J. Clarke managed to exceed the A4’s record speed (but not that of the German locomotive which now held the world record) just as the train approached its destination requiring him to brake hard in order that the train did not overshoot the platform at Crewe.
Just over a year later, the LNER were ready to reclaim the world record from the Germans and the British record from the LMS. On 3rd July 1938, the newly built A4 locomotive 4468 Mallard was hooked to a set of carriages to conduct braking tests. However, the presence of a dynamometer car (carrying speed test equipment) suggested that an attempt on the speed record had been secretly planned, especially considering that the driver chosen to conduct these tests, Joseph Duddington, was renowned within the LNER for his ability to take a locomotive to its limits.
Indeed, on the return run between Grantham and Peterborough, on a straight stretch of track with a slight incline known as Stoke Bank, 4468 Mallard reached a speed of 126 mph. The exertions on the locomotive caused part of a cylinder to melt so after the train limped back to Peterborough, it had another locomotive attached to the front for the journey back to London to receive the plaudits of the press who had been informed of the success. Gresley only claimed a maximum speed of 125 mph, because, he said, the 126mph recorded by the instruments in the dynamometer car could only have been maintain for a few feet. Either way, it was enough to take the official world speed record for a steam train, a record that has remained unbroken for the last seventy years.