London, Brighton & South Coast classes B4 and B4x

The LB&SCR class B4 express locomotives were developed in 1899 by L.B. Billinton because the B2, which had been introduced just a few years earlier, proved to be too weak. Plans were again made to build 25 in Brighton. Since the completion of the third was delayed due to a large backlog of repairs, 25 more B4 were ordered from Sharp, Stewart & Co., all of which were delivered in 1901. Five more were finally built in Brighton in 1902 using boilers supplied by Sharp.

The B4 initially pulled the heaviest express trains until more powerful locomotives appeared in 1912. Between 1922 and 1924, Billinton's son L.B. Billinton had a total of twelve B4 rebuilt with larger superheated boilers and larger cylinders. Because these boilers were too long for the frames, new, longer frames had to be used. Since the locomotives were almost new, they were referred to as class B4x.

Although the boiler of the B4x delivered a lot of steam, it turned out that due to the limited space above the bogie, sufficiently large valves could not be installed and the blast pipe was also not optimally arranged. This meant that they could not fully utilize the steam and timetable speeds higher than 70 mph (113 km/h) could not be scheduled.

The use of the B4 and B4x with express trains ended as early as 1929, so that other tasks were assigned to them. Between 1934 and 1939, 13 locomotives were retired until the Second World War initially stopped this process. Most of the 20 remaining ones came to the British Railways, where all non-rebuilt B4 were retired by May 1951. The B4x followed until December of the same year.