The LSWR gained control of the Southampton Docks in 1892 and within a year, 3 of the B4 tanks were transferred to the docks. By 1900 a further 10 had been transferred to the Southampton docks. They were all painted in a dark green livery and given names generally associated with ports on the Continent with which the LSWR had connections.

In 1907, further locomotives were required by the Docks Department and Drummond built his own version of the class the following year, numbering five locomotives, with differing cab roofs, the Drummond chimney and lack of toolboxes on the tank tops being the obvious differences. These five were nominally class K14, but were grouped with the B4s. Upon delivery, also from Nine Elms, not all were needed at Southampton and three went to Eastleigh for duties.

One curious feature was the lack of any power braking on the B4s when built. Most, maybe all, were fitted with vacuum brake ejectors though the earlier emgines transferred to Southampton Docks had these ejectors removed and relied purely on the hand brake for stopping! In later years the vacuum control was restored.

All passed to Southern Railway control in 1923. The fourteen that had been retained by the Docks Department were painted dark chocolate with red lining, while the remaining 11 received the standard SR lined goods black livery. After 1938, plain black became the standard livery for all members of the class. For most of their pre-war life they were confined to LSWR metals although for a brief period two of them worked the LBSCR Deptford Wharf branch. In 1941, 2 of the class were loaned to the GWR for six months for service in Pembroke Dock, but by 1945 14 of the class were at work in the Southampton Docks.

Because the cost of heavy overhauls was considered by Bulleid to be unjustifiable, he decided to purchase redundant USA Army tank engines for Southampton duties and three B4s were scrapped in 1948 and eleven sold to outside purchasers around the country. For all these 11, their days ended by being cut up on these far-off sites by 1961.

The remaining 11 passed into BR ownership and received several general repairs. Transfers to locations into ex-SEC territory occurred, but all except 30096 and 30102 were scrapped by 1964. These two were sold, the first, N°96 to a subsidiary of Corralls at Southampton to become Corrall Queen. From there, N°96 was sold to the Bulleid Preservation Society in 1972 and was sent to the Bluebell Railway, where to this day it performs invaluable service. No. 102 was sold to Butlins in 1964 to be 'stuffed and mounted' at the holiday camp at Ayr, but it was rescued in 1971 and sent to Bressingham for preservation.