UIC classification of locomotive axle arrangements

The UIC classification of locomotive axle arrangements, sometimes known as German classification or German system, describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 – Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much of the world. The United Kingdom uses the Whyte notation. The United States uses the simplified AAR wheel arrangement for modern locomotives.
Structure.
Garratt-type locomotives are indicated by bracketing or placing plus signs between all individual units.
The most common wheel arrangements in modern locomotives are Bo′Bo′ and Co′Co′.
United Kingdom.
Standard practice in the United Kingdom was to use the Whyte notation for steam locomotives. During World War 2, the Southern Railway used a system modified from the UIC method: Oliver Bulleid, the Chief Mechanical Engineer, numbered the first nineteen of his 4-6-2 "Merchant Navy" class Pacifics 21C1 to 21C19, and the first seventy of his 4-6-2 "West Country and Battle of Britain" class Light Pacifics 21C101 to 21C170, referring to leading axles, trailing axles and powered axles (cf. UIC classification 2′C1′, Whyte 4-6-2). Also, all forty of Bulleid's "Austerity" 0-6-0 "Q1" class were similarly numbered C1 to C40, and his two electric locomotives (later British Rail Class 70) were numbered CC1 and CC2 (UIC classification Co′Co′, Commonwealth Co-Co).