Although A4s were primarily designed for high speed express work they were also capable of high power outputs. In 1940, 4901 "Capercaillie" exerted 2200 drawbar horsepower on the straight and level track north of York when hauling 21 coaches (730 tons gross) at an average of 75.9 mph for 25 miles. On W.A. Tuplin's method for grading steam locomotive performance based on both power output and duration of effort, this was the highest value ever achieved by any British locomotive, at Grade 26.