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The wheel arrangement on large diesel locomotives is described using the UIC classification system, where letters are used to describe the number of axles (as opposed to Whyte notation which describes the number of wheels). Those in use on the SVR are as follows:
*BB: Four powered axles all mounted in the locomotive's frame, driven in pairs, i.e. each pair of axles is connected by driving rods or gears.
The wheel arrangement on steam locomotives and small diesel locomotives is described using [[Whyte notation]].
Oliver Bulleid, the Chief Mechanical Engineer of the Southern Railway, used a modified version of the UIC method to number certain of his steam locomotives. A West Country/Battle of Britain class locomotive would be numbered in a pattern 21C XXX. The first two numbers referred to the number of axles used for leading and trailing wheels, the third letter referred to the number of axles used for driving wheels using the normal UIC classification substitution 1=A, 2=B=2 3=C=3 etc. XXX was the unique identification of the particular locomotive, hence [[SR 34027 Taw Valley | Taw Valley]] entered service as 21C127 and [[SR 34053 Sir Keith Park | Sir Keith Park]] as 21C153.
==See also==
[[Diesel Locomotives]]
