Pacifics Thompson rebuilt a select number of Gresley locomotives that were problematic and had low availability, in addition to attempting to design his own locomotives based on Gresley designs. While Thompson was critical of some of Gresley's design practices, he continued with some design features such as the use of a double Kylchap exhaust and large smokeboxes and his predecessor's influence was still visible in his design. Thompson's Pacific locomotives all retained three cylinders, but with
divided drive and 3 independent sets of
Walschaerts valve gear rather than Gresley's own valve gear design. The outside cylinders were placed behind the front
bogie with the inside cylinder well forward, giving his Pacific locomotives an elongated look which was not commonly seen on the LNER. Claims of Thompson's locomotive underperforming suggests that his designs failed in multiple aspects, with accusations including excessive wheel slip, frame fractures, going against LNER practice and requiring more maintenance. However, Simon A.C. Martin has found no evidence suggesting that they were considered as failures and in cases, contrary to popular claims, found that they were capable and reliable locomotives. While Thompson's Pacifics may have slipped more than other Pacific types on the LNER network due to a poorer weight distribution with a longer frontend, all Pacific locomotives are prone to wheelslip, with Bulleid's Pacifics being just as, if not more infamous for their wheel slip. Thompson also instituted a different maintenance regime for his locomotives where they would be shopped more often for smaller repairs and prevent issues from cascading into major accidents. Despite some faults, Thompson's Pacifics were well designed and retained the ability for high speed running, being able to hold speed in excess of , with design features such as the steam circuit carrying over into Arthur Peppercorn's designs.
Peppercorn's A2 design was a further development of Thompson's A2/3 design, which itself was a development of the A2/2 rebuilt from
Gresley P2s. Under Arthur Peppercorn, some of Thompson's locomotives were fitted with boilers to Peppercorn's design, reviving the "banjo dome" featured on Gresley locomotives.
Class B1 Thompson's most successful design was the two-cylinder mixed traffic
Class B1 4-6-0. The LNER did not have a general purpose mixed traffic engine, such as the highly successful
GWR Hall Class or the
LMS Stanier 5MT Black Fives. The B1 was based loosely on Gresley's
class B17 but omitted the third inside cylinder. The cylinders used were from Gresley's
H3/K2 Class and the boiler was a standard 5 ft 6 in diameter No. 2 boiler. The layout was simplified for easier maintenance and more effective wartime running. The first batch of the Class B1 was authorised in mid-1942, totaling ten with the first being a prototype for further testing. No. 8301 would be frequented by Thompson while under construction, who would ride on the footplate on its first day of operations. It would be named
Springbok out of respect for the visiting
Jan Smuts and South African soldiers. Testing of the B1 would continue well into 1944, comparing it to other locomotives to be replaced. The design proved to be free-steaming, economical and simple to maintain. Construction of the Class B1 was slow beyond the first member, and it took until June 1944 for the other nine members to be completed. More than 400 B1s were built between 1946 and 1952, with
British Railways continuing B1 production after
nationalisation. Up to 409 B1s were available at any time as one was written off and not replaced after an accident. The Thompson B1 equaled the
LMS Black Five locomotives during the
inter-regional exchange trials in the first year of British Railways. Robert Riddles, who would come to design the range of British Railways Standard Classes, praised the B1 for its capability.
Class L1 Thompson's Class L1 were developed due to a demand from the running department for a modern version of the
Metropolitan Railway K class which were reaching the end of their lives. While Gresley
V1 and V3 locomotives were available, they were deemed insufficient. It was ordered in large numbers to serve across the LNER's system as a part of the standardisation scheme. It used an uprated boiler based on the V3 with larger fireboxes and water tanks and B1 cylinders and wheels. Testing under George Musgrave showed they steamed well, had a good reserve of power and accelerated quickly. Initially thirty were ordered and all emerged by 1948. An additional seventy were ordered from
North British Locomotive Company and
Robert Stephenson & Hawthorn and delivered to British Railways. Only when in widespread service did problems with overheating axleboxes appear. Experiments to solve these problems were unsuccessful and the L1s finished their working lives without much modifications or reaching their true potential.
Other rebuilds The
Robinson Class Q4 0-8-0 tender engines were one of the first to be rebuilt by Thompson. Having reached the end of their service life by the late 1930s, most of the class were due to be scrapped. However, with wartime restricting new build locomotives and in need of more powerful shunting engines, Thompson opted to rebuild the design into a tank engine. Most of the old engine, such as the cylinders, motion and boiler, were reused, producing the Thompson Q1, although modifications were made to accommodate an enclosed cab, and the initial 1,500 gallon side tanks were later upgraded to hold 2,000 gallons of water. In 1942, Thompson rebuilt the
Robinson Class J11 and Gresley D49/2 No.365
The Morpeth. The J11/3 was not visually distinct from its original condition, but was modified with new cylinders, valve gears and valve motion, requiring modifications to the engine frames, boiler and chimney. The rebuilding had the desired effect and another thirty were converted, but most of the class remained in their as built condition. The Gresley D49/2 were fitted with Lentz rotary valve gear, but trials proved the piston valve D49/1 to be superior and the D49/2 were due to be converted, save No. 365
The Morperth which was fitted with rotary cam shaft valve gear controlled by steam pressure in 1939. With the camshaft damaged in 1941 and placed in store, Thompson modified it to return it to service. It was rebuilt with two inside cylinders with Stephenson motion, an arrangement similar to the
Robinson Class D11. Although Thompson featured the modified locomotive in his standardisation plans, after trials showed little increase in performance or reliability, the experiment was not repeated and no longer pursued. To boost the amount of available mixed traffic 4-6-0 engines in traffic, Thompson proposed the rebuilding of the
Robinson Class B3. The engines were not particularly successful and had heavy coal consumption, and under Gresley had their valve gear replaced with
Caprotti valve gear. In 1943, No. 6166
Earl Haig was awaiting repairs for its cracked cylinders, and was selected for rebuilding. Again, most of the engine was retained, with a new diagram 100A boiler and outside Walschaerts valve gear fitted, designated the B3/3. It performed well but suffered from cracked frames, and no more were rebuilt, with
Earl Haig being the last of the six members of the class to be withdrawn. The
LNER Class O4 was a heavy goods design originating from the First World War, and the LNER continued to operate a large number of them. While some have already been rebuilt under Gresley, Thompson sought to use them as part of his standardisation scheme. Retaining the frames and wheels, the boiler, cylinders, cab and running plate was modified to create the class O1. Some, where the condition of the cylinders permitted, would not undergo the rather extensive reconstruction and were simply fitted with new cabs and boiler to become the O4/8 subclass. A total of 30 Gresley B17 would be rebuilt to form the B2, with two examples becoming the designated engines for hauling Royal Trains.
LNER Class K4 No. 3445
MacCailin Mor had its middle cylinder removed, becoming the prototype of the
Peppercorn Class K1, designated the K1/1. Similarly, a K3 had its middle cylinder removed to become the K5, easing maintenance.
Coach design Thompson improved passenger safety by introducing steel-bodied
coaches to the LNER. Previously the LNER had
Gresley-designed coaches, the most famous of which had
teak bodies but by 1940s standards these were considered insufficiently safe in a collision. Therefore, during the
Second World War Thompson designed new all-steel coaches that became a forerunner of
British Railways Mark 1 design. == Controversy ==