The diesel locomotives later called class 24 were designed as a part of the 1955 modernisation program and initially carried numbers starting with D5000. Their second name “Sulzer Type 2” gives reference to the origin of the diesel engine and the power class. One requirement was that as many parts as possible could be taken off the shelf from the industry.

The engine of type 6LDA28 was a direct-injected and turbocharged six-cylinder that was the same as in the CIÉ class 101, but with an increased output of 1,160 hp. Other parts like the generator, traction motors, brakes, multiple working equipment and steam heating boiler were also taken from existing types. On the cab ends they had gangway doors, but as in other locomotives they were rarely used and later got sealed.

Some belonged to the lighter subclass 24/1. These had smaller fuel and water tanks to increase their route availability in the Scottish highlands. Most class 24/0 and 24/1 locomotives later lost their steam heating boiler when they were no longer used in passenger service. They were withdrawn between 1973 and 1980. Today, four are being preserved with all of them again carrying their pre-TOPS numbers.

In order to be able to test two-stroke diesels as part of the British Railways' modernization plan, the class 28 with the Crossley HST was ordered from Metropolitan-Vickers. This had eight cylinders in V-shape and exhaust pulse pressure charging. This engine had already been used in the Irish class A and the WAGR class X. What was special was the asymmetrical underframe with a two- and a three-axle bogie, which led to the Co-Bo wheel arrangement.

The class 28 got the nicknames “Metrovicks”, “Crossleys” and “Co-Bos”. One problem was the windows in the driver's cab falling out, which could be resolved. However, the engines caused bigger problems. In addition to excessive exhaust plumes, this was primarily due to insufficient reliability, which led to many failures. That's why they were often used double headed so that they could continue running if one locomotive failed. Like other British diesel locomotives with non-standard engines, they were retired between 1967 and 1968.

The life of the Class 31 actually began as the Class 30, also known as the Brush Type 2. These locomotives used from October 1957 were six-axle engines with four powered axles, fitted with a Mirlees JVS12T with 1,250 or 1,365 hp. The carrying axles were in the middle of the bogies and had a wheel diameter of 3 ft 3.5 in, while the driven wheels had a diameter of 3 ft 7 in. Since the Mirlees engines did not prove themselves, an engine was equipped with the engine of the class 37 in 1964. Since the full power could not be used with four traction motors, the engine was used without an intercooler with an output of 1,470 hp. Since this combination was significantly better, between 1965 and 1969 all remaining 262 pieces were converted in the same way and were then listed as Class 31.

The first batch still had a top speed of 80 mph and electromagnetic controls for multiple working. Later locomotives received electro-pneumatic control gear and were designated as class 31/1, the first batch was subsequently renumbered to 31/0 to distinguish them. The top speed was soon increased to 90 mph. The boxes for displaying the running numbers were placed above the cab windows and the first batch without these boxes soon became known as the “Skinheads”. Since the locomotives had steam train heating, they were used in front of passenger and freight trains. The operations took place primarily on branch lines or as reinforcement with light trains. Later, 70 locomotives were equipped with electric train heating and designated as Class 31/4. Since these diverted up to 330 kW from the engine power, which was not very high anyway, these locomotives were mostly used to assemble and preheat passenger trains.

Network Rail 31233 in August 2013 with a test train at Shrewsbury

Peter Broster

From the moment the DMUs of the Sprinter series took over the light passenger train services in the 1980s, the class 31 was almost exclusively used for freight trains. In most cases, the lines for train heating were removed to prevent the locomotives from being temporarily borrowed out to the passenger train division. After privatization, the locomotives came to many different operators. They are used there, for example, to provide additional power for passenger trains. For this purpose, the lines for the train heating were routed through some locomotives without the power having to be diverted from the locomotives themselves. Other examples were used in top-and-tail operation, i.e. as a passenger train with one locomotive each at the front and rear to replace unavailable railcars. Such operations could and can be observed with various older diesel locomotives since privatization. Network Rail, the operator of the UK rail network, uses the Class 31 for test trains across the network. These can be recognized by the completely yellow paintwork on the locomotive and wagons. About 26 examples were bought for operation on museum railways.

The BB 63000, which was known as the 040 DE before it was redesignated in 1962, was created to replace medium-powered steam locomotives. They were four-axle diesel-electric locomotives with one driver's cab and asymmetrical hoods. A six-cylinder inline engine from Sulzer was used as the power plant, which delivered 600, 725 or 750 hp depending on the production batch. 250 examples of this series were built, but there were also almost identical locomotives in other railway administrations, which were either delivered from France or were manufactured under license. These were the class 850 in Luxembourg, the class 642 in Yugoslavia, the class 10700 in Spain (later renumbered 307) and the class 1200 in Portugal. The BB 63400 and 63500 are variants with a V12 engine from the Société Alsacienne de Constructions Mécaniques (SACM). Of the latter, 603 pieces were made.

The locomotives were also called “Deux Cheveaux” due to their large number and their wide range of applications in reference to the also ubiquitous Citroën 2CV. Although the design with a single driver's cab is more associated with shunting locomotives in Germany, they were also used in mainline service with passenger and freight trains. After a few decades in service, the area of application shifted to freight trains and finally they were used almost exclusively for shunting tasks and with work trains. The Sulzer locomotives were phased out by 2006, but 61 of the SACM locomotives were still in use at the end of October 2019. A total of 23 units were converted into the BB 64700 shunting locomotive between 1989 and 1993, with new MTU 8V 4000 engines. In another 19 units, the diesel engine and driver's cab were removed and the frame was shortened so that they now only have the traction motors. These vehicles, designated as TBB 64800, were each coupled to a BB 64700 and received the power for propulsion from their diesel engine.

As a stronger addition to the BB 63000, the BB 66000 was created with basically the same structure. The first 40 locomotives still bore the designation 040 DG and were re-designated in 1962, a total of 318 units were built. While the BB 63400 and BB 63500 got a V12 engine from SACM, the BB 66000 had a V16 from the same family with 1,400 hp. The first engines were delivered with a top speed of 105 km/h, but they were soon subsequently approved for 120 km/h and all others as well ex works.

From 1968, 106 BB 66400 were built, which were based on the latest BB 66000 series and were equipped for electric train heating. Already between 1960 and 1962 13 BB 66600 had been completed, which had a Pielstick engine. The first three of these were created by conversion and ten others were newly built. Between 1985 and 1991 a total of 34 BB 66000 were equipped with the same engine and designated BB 66700. They had a modified gear ratio for 80 km/h in order to increase traction and use it for shunting.

The locomotives were initially used in regular service with passenger and freight trains. Like the BB 63000, they were considered “jack of all trades”. The capabilities for multiple working were somewhat limited, since the sub-series were partly not compatible with each other. Over time, the engines were phased out of passenger service and were primarily only used for lighter freight trains.

In 2005, a total of 91 locomotives were fitted with new MTU 12V 4000 engines to extend their service life. In 2019, 64 of these were still in use, mainly in the SNCF freight and infrastructure areas. The BB 66600 with Pielstick engines had already been retired in 1997 and the last BB 66700 disappeared in 2018. At that time some of the unconverted locos with SACM engines were still assigned to the STF Infrarail.

The class 001 designates six-axle diesel-electric locomotives originally fitted with 1,200hp Crossley two-stroke diesels. They were intended for passenger and freight service and were built by Metropolitan-Vickers in Manchester. The low reliability of the Crossley engines meant that from 1968 they were rebuilt to engines of the EMD 645 type. These also worked on the two-stroke principle and initially produced 1,650 hp. Since the propulsion electronics and the cooling system were stressed with this power, the power was soon reduced to 1,325 hp. The 60 locomotives provided valuable services until they were replaced by new class 201s in 1994.