On 3 July 1938 4468 "Mallard"; the first of the class to enter service with the Kylchap exhaust, pulling six coaches and a dynamometer car, set a world speed record (indicated by the dynamometer) of . Gresley never accepted it as the record-breaking maximum. He claimed this speed could only have been attained over a few yards, though he was comfortable that the German speed record of had been surpassed. Close analysis of the dynamometer roll (currently at the NRM) of the record run confirms that "Mallard"'s speed did in fact exceed that of the German BR 05 002. The "Mallard" record reached its maximum speed on a downhill run and failed technically in due course, whereas 05 002's journey was on level grade and the engine did not yet seem to be at its limit. On the other hand, the German train was four coaches long (197 tons), but Mallard's train had seven coaches (240 tons).