[2] They were designed to be lighter in weight than their sister locomotives, the Merchant Navy class, to permit use on a wider variety of routes, including the south-west of England and the Kent coast.

A total of 110 locomotives were constructed between 1945 and 1950, named after West Country resorts or Royal Air Force (RAF) and other subjects associated with the Battle of Britain.

Due to problems with some of the new features, such as the Bulleid chain-driven valve gear, sixty locomotives were rebuilt by British Railways during the late 1950s.

[6] At the same time, there would be a continuing need for fast freight locomotives, capable of operating on both electrified and non-electrified routes, without impeding the intensive use of the system by passenger trains.

Although Bulleid built two prototype electric locomotives in 1941, these were, as yet, unproven, and freight haulage would be undertaken by steam traction for the foreseeable future.

The earliest drawings were for a moderately sized 2-6-0 with similarities to the London and North Eastern Railway K4 class, which Bulleid had helped design for the West Highland Line when he was Nigel Gresley's assistant.

Based on the mechanical experience gained from the Merchant Navy locomotives, Bulleid incorporated his chain-driven valve gear into what became the new design.

[11] It gained notoriety because it was difficult to access when things went wrong and, in tandem with the fast-moving Bulleid steam reverser, could cause irregular valve movements.

According to Creer it was intended to be an aid in cleaning the locomotive with carriage washers to reduce labour requirements during the post-war period,[12] whereas Bradley asserts that the intention was to lift the steam and exhaust gases away from the cab.

Other refinements and innovations used on the Merchant Navy class included steam-powered clasp brakes and the unusual 6 ft 2 in (1.88 m) Bulleid Firth Brown (BFB) wheels.

[1] As with the Merchant Navy class, the water tank was of welded sheet construction to save weight, and the tender was fitted with vacuum braking equipment of a clasp-type similar to that on the locomotive.

These were identical to the West Country class and the new designation was purely concerned with giving the locomotives names that befitted their intended allocation to the Eastern Section.

[18] By the time of the nationalisation of British Railways in January 1948, seventy Light Pacifics had been built at Brighton Works, with a fourth batch of twenty on order.

34110 66 Squadron, in January 1951 was delayed for several months pending consideration of proposals from British Railways management for a major modification to a standard two-cylinder design without the chain-driven valve gear,[22] but the locomotive entered service as Bulleid intended.

21C166–21C170 were fitted with TIA ("Traitement Integral Armand") chemical feed-water equipment that precipitated scale-forming constituents in the hard water of southern England into a non-adhesive mud that could be cleared using a manual "blow-down" valve.

[10] This coincided with the removal of the tender "raves" on all but five locomotives, as they obstructed the packing of coal into the bunker and restricted the driver's view when reversing.

[28] The resultant "cut-down" tender included new, enclosed storage for fire-irons and glass spectacle plates to protect the crew from flying coal dust when running tender-first.

This plaque was mounted on the casing between the gunmetal locomotive nameplate and the West Country Class scroll, above the middle driving wheel.

[35] Once it became clear that the locomotives would be used further afield than the West Country, a decision was made to name the remainder after RAF squadrons, airfields, commanders and aircraft that had participated in the Battle of Britain over Kent, Surrey and Sussex.

The first locomotives constructed by British Railways were of the Battle of Britain class, but the naming policy reverted to the West Country for Nos.

[38] As with the Merchant Navy class, they could generate great power using mediocre quality fuel, due largely to Bulleid's excellent boiler.

[39] These may be summarised as follows: Restricted driver visibility was mentioned in the report on the disastrous Lewisham rail crash on 4 December 1957 outside St John's railway station, in which 90 people were killed and 173 injured.

[19] The rapid onset of the 1955 Modernisation Plan during the early 1960s meant that the remaining fifty locomotives were not rebuilt, and continued in as-built condition until withdrawal.

[10] Eleven of the surviving engines are named after West Country locations in the South of England and the remaining nine after RAF Squadrons or significant persons, including Prime Minister Winston Churchill.

The class has proved to be useful for preservation societies, due to its good route availability and ample power, with some having returned to the main line to haul special trains.

[76] Bulleid advocated a continental style of numbering, basing this upon his experiences at the French branch of Westinghouse Electric before the First World War, and his tenure in the Railway Operating Division (R.O.D.)

[80] The rebuilt locomotives were also in British Railways Brunswick green with orange and black lining, and crest on the tender side, whilst the nameplates were placed on a custom-made mounting on the running plate due to the absence of a flat surface.

[6] The use of welded steel construction and the various innovations that had not previously been seen in British locomotive design meant that the class earned Bulleid the title "Last Giant of Steam".

A great deal of money was wasted on resolving the problems of a class designed for duties that could have been undertaken by cheaper 2-6-2 or 4-6-0 mixed-traffic locomotives.

[10] A curious but common sight west of Exeter during the winter months was a Light Pacific hauling a local stopping service with a single carriage to destinations as diverse as Padstow and Wadebridge.