 The Swing Door trains were originally and steam-hauled bogie passenger cars, the majority of which had been built between 1887 and 1893.When converted to electric traction between 1917 and 1924, the cars were extended by two compartments to a total length of , and then fitted onto new under-frames and bogies.The conversion process was suddenly halted in 1924, with partially-converted cars being patched up and returned to service with their original codes and numbers.