 X37 was equipped with a booster in March 1932, however X36 was never fitted with one, even though its trailing truck axle was equipped with the necessary pinion gear wheel.The success of the original eleven locomotives delivered in 1929 (X27 to X37) led to further examples being built.X38 was assembled in 1937 from spare parts, helping to create work for workshops staff at a time of high unemployment.