 With their ability to travel at relatively high speed and their low axle load, the D3 helped to speed up passenger services on many lightly laid branch lines.In the period 1922-1927 well over half the fleet of DD engines were renumbered, some twice, to clean up the mess left behind by the former odds/evens system and group engines of the same design into a consecutive series.In 1922 the proposed range was 490-799 for the Dd engines and 250-269 for the formula_1s, although in practice the ranges ended up as 500-799 and 250-287 with many numbers unfilled.