Since at the beginning of the 1920s the Atlantic express locomotives of the Great Northern Railway could no longer cope with the increasing train weights, Sir Nigel Gresley began to develop a Pacific locomotive. The first attempt to expand the Atlantics with another coupled axle was quickly dropped. Gresley eventually took inspiration from the Pennsylvania Railroad's K4 and developed a locomotive that just barely fit into the gauge and weight limits.

Schematic drawing of the A1 with dimensions

Locomotive Magazine, May 1922

From the American locomotive he took over the large firebox, which was mounted above the trailing axle, a roof of the firebox that sloped towards the rear and a boiler that tapered towards the front. What was new was the introduction of a combustion chamber, which at the same time limited the length of the smoke tubes to a tolerable level. There were three cylinders, all acting on the second coupled axle. So that the inner cylinder did not get in the way of the front coupled axle, it together with the associated connecting rod were tilted upwards by about seven degrees. Furthermore, Gresley's valve gear was used, which did not require any control mechanism on the inside and instead transmitted the valve movements of the outer cylinders to the inner cylinder via a lever mechanism.

A3 No. 4472/60103 “Flying Scotsman” in York

Train Photos / 60103 Flying Scotsman at York NRM

The first two locomotives with the numbers 1470 and 1471 were completed in 1922 and formed the basis for the production machines. These were not completed until after the 1923 grouping and were given the class designation A1 by the LNER. Although they were actually developed for the GNR, they were used throughout the LNER network. The locomotives that were to cover longer distances were given a four-axle tender. The locomotives for the Flying Scotsman were given new types of corridor tenders, which allowed passage to the train. In order to achieve the long non-stop routes, various improvements were made to some locomotives, which were mainly in the area of control. Soon the boiler pressure was also increased from 180 to 220 psi. One of these locomotives was the first to achieve a proven speed in excess of 100 mph as the 1904 record of GWR 3700 No. 3440 “City of Truro” is not confirmed with certainty. Later, 108 mph were also reached.

A3 with corridor tender

Die Lokomotive, November 1928

Based on the subsequently introduced improvements, the further developed A3 was built from 1928. It also had a boiler pressure of 220psi, optimized valve gear and lubrication, better weight distribution, and slightly smaller cylinders with a higher degree of superheating. The driver's seat was moved from right to left to allow a better view of the trackside signals. The conversion of the existing class A1 locomotives soon began, but this took until 1949. This resulted in a total of 51 converted A1 and 27 newly created A3. In 1945, Gresley's successor, Thompson, significantly modified an A1 into a one-off A1/1.

Around 1960, the locomotives, which were still almost complete, were modernized further. This included a double Kylchap exhaust system and various smoke deflectors. This should allow the machines to keep to the same timetables as diesel locomotives, but their number thinned out noticeably from 1962 and the last example was retired in 1966. Today, the A3 4472 “Flying Scotsman” is the only one preserved. After undergoing a major overhaul between 2006 and 2016, it is back in service and bears the BR number 60103, which it received in 1948.

Gresley developed the Class A4 locomotive for the “Silver Jubilee” express train, which consisted of specially developed articulated cars. It was based on his A3 and was streamlined. Like this, it had three cylinders, but a higher boiler pressure and further optimizations within the boiler. What was striking was that the axles were in conventional friction bearings, as the initially planned German roller bearings could not be used for political reasons.

“Union of South Africa” with streamlining cut out for easier maintenance

Andy Hawkins

The “Mallard” achieved particular fame because on July 3, 1938 it reached the still official world record for steam locomotives at 125 mph (201.2 km/h), which is controversial. It was reached on a slight down gradient and resulted in damage to a connecting rod bearing, while higher speeds on the flat were unofficially recorded in other countries. Today there are still six A4s, three of which are still operational. Among the ones that still exist today is the “Mallard”, which is not operational.

The class A8 of the LNER was created when Gresley rebuilt all 45 locomotives of the North Eastern class D, the later LNER class H1 that had been designed by Vincent Raven. To make this 4-4-4T better suited for heavy suburban traffic and long distance coastal trains, he swapped the two-axle trailing bogie against a single axle and added another driving axle, making it a 4-6-2T.

In this process, also the boiler was revised. It was now operated with 175 instead of 160 psi and had a Robinson superheater instead of the Schmidt type. After all had been rebuilt between 1931 and 1936, they also replaced the 0-4-4T class G5. The introduction of the DMUs in the 1950s was the decline of the A8. They were withdrawn between 1957 and 1960.

The LNER originally planned a locomotive with a 2-10-0 wheel arrangement as a more powerful successor to the GNR Class O2. Ultimately, the two class P1 locomotives were built in 1925 and had the wheel arrangement 2-8-2. To increase tractive power, they had three cylinders and an additional booster on the trailing axle. The tractive power was sufficient for trains with 100 coal cars, but due to their length they caused problems in the operational process and meant that there was no series production. Because the boosters consumed too much coal and steam was leaking into the cab, they were removed in 1937 and 1938. In 1942 both locomotives were rebuilt to class P1/2, with smaller cylinders and higher boiler pressure. Immediately after the end of the Second World War, they were scrapped because the decline in freight traffic meant that there couldn't be found another area of use.

For the difficult LNER line between Edinburgh and Aberdeen, Gresley designed the 2-8-2 express locomotive of the class P2. Being the only eight-coupled express locomotive regularly used in Britain, this allowed enough traction on heavy trains on the grades which reached up to 1.34 percent. Only six were built which got names from Scottish lore.

The first one built in 1934, No. 2001 “Cock o' the North”, got Lentz poppet valves and a double Kylchap exhaust. All others received a more conventional Walschaerts valve gear. Also the first later got this type of valve gear. The last four had a longer firebox and there were also changes in production due to problems with smoke lifting. In 1936, they got streamlined fronts.

No. 2006 “Wolf of Badenoch”

flickr/Historical Railway Images

Due to reliability issues originating from the difficult maintenance under war conditions, Thompson rebuilt all six P2 into A2/2 Pacifics in 1943 and 1944. So no P2 is preserved, but today there are two undertakings which are building a new P2 each. One will be non-streamlined and called 2007 “Prince of Wales”, while the other will be called 2001 “Cock o' the North” and be streamlined, like the original 2001 after it had been rebuilt.

Gresley developed the V1 as a powerful tank locomotive for suburban lines. Its drive consisted of three cylinders cast in one piece. Between 1930 and 1939, 82 V1s were built, which were initially used in the Glasgow and Edinburgh area. Ten V3s were then built, which had 20 psi higher boiler pressure. From 1948, a total of 71 V1s were converted to V3s by the LNER and British Railways. The decommissioning took place between 1960 and 1964.

For fast mixed traffic, Gresley took his A1 and A3 Pacifics, shortened the boiler, switched the two-axle leading bogie for a single axle and fitted smaller 6 ft 2 in (1,880 mm) driving wheels. So they still had three cylinders, which were cast in a single piece. The LNER designated these locomotives class V2, while the first one numbered 4771 was named “Green Arrow” after a prominent express goods service.

They became the only successful British 2-6-2 tender locomotives and were not much slower than the Pacifics. Although their axle load of 22 tons limited their area of operation, their most suitable roles were the service with fast goods trains and very heavy expresses. In service they sometimes reached speeds of 90 mph, while one locomotive was even credited to have exceeded 100 mph on a test run.

Between 1936 and 1944, a total of 184 were built in Doncaster and Darlington. They fulfilled very important duties in World War II, but due to the reduced track maintenance the leading bogie had to be replaced by a new one. After less successful experiments with double chimneys in 1960, eight got a Kylchap exhaust. These had performances on par with the Pacifics and were thus called “Super V2”.

However, Thompson's 4-6-0 class B1 had superseded the V2 in mixed traffic and became the new LNER standard locomotive in this role. The V2 were withdrawn between 1962 and 1966. 4771 “Green Arrow” is the only one that was preserved. It was operational until 2008 and is still waiting for a boiler overhaul.

In 1929, Gresley attempted to build a high-pressure locomotive using the Yarrow boiler from shipbuilding. This boiler consisted of three barrels arranged in a delta shape and was not divided into a firebox and a boiler barrel. It was faired with a streamlined mantle and operated at 450 psi. The chassis came from an A1 Pacific and was expanded to include an additional, independently movable trailing axle. A four-cylinder compound engine was used, which had relatively small cylinders due to the high pressure. Since the boiler did not meet the expectations placed upon it, the locomotive was rebuilt with a conventional boiler in 1936 and was given three cylinders of the same size.

The K1 was a mixed traffic locomotive designed for the LNER, but was only delivered directly to British Railways in 1949 and 1950. Since Edward Thompson was a fan of two-cylinder locomotives, he rebuilt a K4 from three to two cylinders in 1945. Since the new cylinders were only slightly larger than the old ones, he increased the boiler pressure to keep the loss of tractive power to a minimum. This prototype was designated K1/1 and was considered a success.

Series production of 70 K1s did not begin until 1949, when Arthur Peppercorn was chief engineer of the Eastern and North Eastern Region of British Railways. Compared to the prototype, he had made some changes, which included improvements to the firebox and the suspension of the leading axle. He also now used a tender with a water capacity of 4,200 gallons instead of 3,500.

The K1s mostly remained in service in the area of the former LNER. With a maximum forward speed of 50 mph and reverse 45 mph, they were used on all types of trains, including express trains. Their withdrawal took place between 1962 and 1967. Only the 62005, which has been operational again since 1975, has been preserved. It wore LNER livery most of the time with the imaginary number 2005, which is historically incorrect.