The last two of the 842 LMS Stanier Black Fives, numbers 44686 and 44687 were constructed by British Railways at Horwich Works in 1951.
44686 and 44687 differed from other members of the class in a number of respects. They, like 1948-built 44738-57 featured Caprotti valve gear. Unlike all of their predecessors however they had a high running plate. This gave them a distinct appearance that was very American in character. The pair also featured a double chimney and had Skefco roller bearings on all axles.
The Caprotti valve gear differed from that fitted to previous Caprotti black fives. The British Caprotti valve gear was a new development of the Caprotti valve gear by the Associated Locomotive Engineers, under the leadership of L.A. Daniels.
44686 and 44687 emerged from Horwich works in April and May 1951 respectively. For much of their lives they were allocated to Longsight. 44686 was withdrawn in October 1965. 44687 was withdrawn (when?). Both were scrapped.
in the early 1960s both 44686 and 44687 worked off Southport shed (code 27C) on passenger trains from Southport to Manchester and Rochdale via Bolton. Other non-standard LMSR 5MTs were at Southport including LMSR Caprottis and the unique Stephenson Link machine 44767.
The success of the British Caprotti valve gear lead to its fitting to the final batch of BR standard class 5s and also to the solitary BR standard class 8 71000 Duke of Gloucester. One of the Caprotti standard fives survives(73129), as does The Duke.