The first batch of Caprotti Black Fives, M4748–M4750, emerged from Crewe in February 1948. A second batch, M4751–M4752, entered traffic in March 1948, followed by nos. 44754 and 44755 in April, 44756 in June and 44757 in December. Caprotti valve gear had previously been fitted to a batch of twenty Black Fives,
nos. 44738-57, built in 1948. The valve gear on these was driven by one drive-line between the frames, driven from the leading coupled axle. This necessitated the boiler be raised by to . The smokebox was extended by and the chimney moved forward to allow room for the Caprotti valve box and associated steam and exhaust pipes. The large steam pipes are an obvious visual recognition feature. The locomotives fitted with Timken bearings had large split
cannon-type axleboxes between the frames. To allow room for the firebox between the middle and rear axleboxes the spacing between the driving and rear coupled wheels was increased from to . This gave a longer wheelbase of as against the of the standard locomotives. The locomotives with plain bearings also had the longer wheelbase. All locomotives had a modified cab and a lowered running plate, necessitating the use of
splashers over the wheels. In service, the Caprotti Black Fives were slow in acceleration, but were powerful at high speeds, and coasted freely. The slow acceleration was caused by inefficiencies in the drive and valve events. These were addressed in the design of the last two Black Fives to be built,
44686-7, which emerged in 1951 with Caprotti valve gear driven by two external shafts on either side of the locomotives. and it was also employed on the
standard class 8 71000 Duke of Gloucester. 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. ==Withdrawal==