the numbering block from 5500 was allocated to the Patriot Class, a further batch of 200 locomotives were numbered from 4800 to 4999, followed by a batch from 4658 to 4799. By this time the LMS had been nationalised, and British Railways added 40000 to all numbers. Eventually the 842 examples would number 44658–45499. Ivatt engines and experimental modifications From early 1947, engines were built with the top feed on the front ring of the boiler (from no. 4998), and Nos 44758-767 had a longer wheelbase (27 ft 6in rather than 27 ft 2in, with the change in the coupled wheelbase from 7 ft + 8 ft to 7 ft + 8 ft 3in); this was necessary in order to accommodate the Timken roller-bearing housings without fouling the ashpan. In 1948, George Ivatt introduced more modifications to bearings and valve gear; other experimental Ivatt features included the use of steel rather than copper fireboxes on certain engines, and the fitting of double blastpipes & chimneys in some instances. 44738-57 were built with Caprotti valve gear. The last two, nos. 44686 and 44687 built at Horwich in 1951, were fitted with a new arrangement of Caprotti valve gear, which was later used on some of the BR standard Class fives, and the BR class 8 4-6-2. No. 4767, built at Crewe and delivered in December 1947, had outside Stephenson valve gear: instead of eccentrics, double return cranks were used to drive the eccentric rods, and a launch-type expansion link was used. This one cost £13,278, which was about £600 more than those built at the same time with Walschaerts' valve gear. The aim of the experiment was to find out if a valve gear having variable lead (as opposed to the constant lead of the Walschaerts' motion) would affect performance. On trial, it proved to have no advantage, although in normal service it did gain a reputation as a good performer on banks. Accidents and incidents On 13 October 1939, locomotive No. 5025 of the class was hauling an express passenger train from Euston to Stranraer (pilot to engine 6130) when it was in collision with locomotive LNWR Class G1 9169 which was attaching a van to the rear of an Inverness train at , Buckinghamshire, severely damaging it. Five people were killed and more than 30 were injured. No. 5025 was repaired and survives at the Strathspey Railway. In 1941,