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What is the difference between 45xx Class and Class 45?

The question: What is the difference between a 45xx Class and a Class 45? should really be: What isn't the difference?
Just about the only things they have in common is that they are both railway engines and they both operated in Great Britain (and possibly the number 45).
The 45xx was a small Great Western Railways (GWR) tank engine often referred to as a Small Prairie. They were built between 1906 and 1924 and could often be found on West Country branch-lines. The xx in the class name was used in place of the locomotives unique two-digit identification number to refer to the class as a whole rather than any one locomotive. 
The Class 45, in contrast, was a large main-line diesel-electric engine built between 1960 and 1962 and operated on the Midland Main Line until being displaced by HSTs in 1982. 
So why did the railway companies allocate the two locomotives the same or at least a very similar classification?
The truth is they didn't. When diesels were first introduced they were given a classification type, the Class 45's were one of many type 4's. Their numbers were displayed with the prefix D for diesel, followed by between 1 and 3 digits to identify individual locomotives.
So in the dawn of diesel different types of traction and classes could not be confused, however, the railways faced a much bigger problem, and that was keeping track of locomotives and their maintenance. As engines moved around and work was carried out at various locations, the engines paperwork would become spread across the country. To solve this problem the TOPS system was introduced.
TOPS (Total Operations Processing System) is a computer system that allows all a locomotives paperwork to be held in one place and accessed remotely.
For this system to work however the whole way in which engines were classified and numbered had to be re-thought. It was decided that all diesels would be allocated a class between 1 and 79, the higher the number the more powerful the locomotive, and with there being so many types of locomotives around the power rating in the forties it was inevitable that a Class 45 would be created.
In reality, there never was any confusion between the two classes because the 45xx Class were all retired long before the Class 45's appeared on the tracks.
I would advise though that you enter the details very carefully when shopping on the internet for your new model of a 45.
Posted in: Model Railway, Rolling stock

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