The London and South Western Railway made the jump from the 4-4-0 locomotive to the 4-6-0 in 1905 with the F13 class. The trigger for this were the so-called “Boat Trains”, which had to bring a constantly growing number of passengers with ever faster schedules to the ships on the English Channel coast. Since use was only to be expected on main routes, the designer Dugald Drummond hardly had to comply with any axle load restrictions. Due to the increased number of axles and the greater overall length, a significantly stronger boiler than on previous locomotives was possible. In order to exploit its capacity, a non-compound-action four-cylinder engine was used. Up to this point in time, engines with four cylinders were mostly only used in compound locomotives. Since the LSWR did not use water troughs to fill up during the journey, four-axle tenders with a correspondingly large capacity were used.
Schematic drawing with dimensions
Locomotive Magazine, March 1921
Only five examples were built in 1905 in the LSWR workshops in London's Nine Elms. Although these locomotives looked very simple on the outside, the running gear was overly complex. The outer cylinders had Walschaerts-type valve gear, while the inner ones were controlled by their own Stephenson-type valve gear. The service with the Boat Trains between Salisbury and Exeter lasted only one year and was then discontinued. They were now repurposed as freight locomotives and henceforth had to haul coal trains between Salisbury and Southampton. One locomotive was fitted with the Eastleigh superheater introduced on the H15 in 1920, but this did not quite make up for the general weaknesses of the class. Eventually, all five F13s were converted to H15s starting in 1924.