The Brush type 4/class 47 is, put simply, THE definitive post modernisation plan/second generation mixed traffic diesel electric locomotive and the certainly the only type produced in a large quantity. Despite problems that have dogged the class throughout its service life the fact that they are still in service in quantity (still greater than newer classes including - just, but not for much longer - the class 66) almost 40 years after their first introduction has to be a measure of their success.

The origins of the class come from the Eastern Region declining an offer of allocations of the Peak class because they had reservations about the 1Co-Co1 wheel arrangement and they also preferred a locomotive of a greater horsepower. The Eastern Region had developed a good relationship with Brush during the production of the type 2 to 4 A1A-A1As (subsequently class 31) and this spurred the company to develop a new locomotive for them based around the Peak class equipment. It was the uprating of the Sulzer engine used in the Peaks to 2750 hp that allowed the project to gain momentum not only with Brush but also with other manufacturers competing for the large order of what was emerging as being about 500 locomotives. Brush emerged as the strongest contender and they offered BR a range of alternative designs, some, but not all, based on existing Peak class equipment. A Co-Co design with a new flat fronted load bearing body but using the existing Peak class equipment package was selected. In fact the first 20 used equipment originally intended for part of the final batch of the Peak class.

The agreement between BR and Brush included construction of the design using Brush electrical equipment under licence in BR works. In total 512 locomotives were built, 310 by Brush at Loughborough and 202 at BR's Crewe works.

With the benefit of hindsight not enough attention was paid to future needs in the specification which perhaps relied too much on the status quo therefore requiring future modifications. Whilst the first 20 were built with ETH subsequent constructions did not. Also subsequent modifications were required to provide air/dual braking for freight and Mk2 coaches. It is in these respects that the contemporary - and Southern's exclusive (at the time) - BRCW type 3 (class 33) was more far sighted.

The class was plagued by unreliability in its early days. The choice of the uprated Sulzer prime mover proved to be a mistake. There were problems with the fabricated crankcases and internal joints which required rewelding and rebalancing. These measures led ultimately to a reduction of engine speed and maximum engine output. There were also problems with fractures and traction motor fires in the well proven but heavyweight manganese cast steel Commonwealth bogies. However the major problems were resolved by 1969 and the class settled down to become the mainstay of the type 4 diesel electric fleet for over three decades.

The class has been used system-wide although due to the Southern's native fleet of class 33 diesels the type has not been as closely associated with operations in the south as elsewhere except perhaps comparatively recently. The class was used in 1967 on the later operations of the Bournemouth Belle when management dogma prevented "last-gasp" use of steam locomotives on the prestigious service (so prestigious that they were within a mater of months to withdraw it!). Thereafter the class was not regularly used on purely Southern passenger services until the introduction from the early 1990s of 47/7s (having been cascaded from Scotland by the introduction of class 158s there) on the Waterloo-Exeter service. This was a stop-gap measure to replace the ailing (and slightly younger) class 50s on this route until the 47/7s were in turn replaced from 1992 by the class 159s. The class has been regularly associated with the Southern throughout its entire life on inter-regional passenger services (today with Virgin Cross Country), special workings and inter-regional freight, especially Freightliner services.

47/0 Largely as originally constructed. Steam heating (isolated) or no boilers
47/3 No train heating. Prime work freight duties. Some fitted with slow speed control for MGR
47/4 Electric or dual train heating
47/6 one off experimental conversion using a 3,250hp English Electric engine - test plant for class 56 prime mover, later converted to 47/9
47/7 modification of 47/4 for push-pull working originally for Edinburgh-Glasgow shuttle services
47/8 officially 47/4s but widely referred to as 47/8 Modification of 47/4s with long range (twin) fuel tanks
47/9 one off experimental conversion using a 3,250hp Ruston-Paxman engine - test plant for class 58 prime mover, converted from class 47/6

Mention should also be made of short lived class 48, five locomotives fitted with a French-built Sulzer 12 cylinder V type engine. These were converted to class 47s in 1969. Finally and much later the class 57 is a rebuilt 47 using a refurbished General Motors type 645 prime mover. Introduced in 1997, the class 57 promises to prolong the 47 design whose numbers have otherwise been dwindling in the last decade and the remaining members (about 50% of the original) can only have a few years left.