- ‘D’ 0-8-0 Locomotive class
- After Whale
 had rebuilt a number of ‘A’ class 3-cylinder simple 0-8-0 goods engines into class ‘C’ simple engines by fitting new inside cylinders and Joy’s valve gear, it was decided that their cylinders were too large for their original boilers. Sixty three were therefore fitted with 5ft 2in diameter boilers similar to those used on the ‘Experiment’ class 4-6-0 engines. In 1911 these became known as class ‘D’. 
- Dock Tank 0-4-2T Locomotive Class
- See Bissell Tank
- Dreadnought Locomotive Class
- Designed by F.W. Webb, the ‘Dreadnought’ class was basically an ‘Experiment’ enlarged to produce more power. The boiler was larger, with 176 psi instead of 150 psi, and the valve gear was modified. In many ways the ’Dreadnought’ was the first modern Webb engine. In addition to a circular smoke box door, tommy-bar screw coupling, it was the first engine to have the new 3in thick tyres made of steel.
- ‘DX’ 0-6-0 Locomotive Class
- The ‘DX’ 0-6-0s were designed by John Ramsbottom, and incorporated all the usual Ramsbottom features; his own design of chimney top, safety valves and screw reverse, horizontal smoke box door, coupling rods with split ends and wedge adjustment, slotted splashers wooden buffer beams and brake blocks, no brakes on the engine and green livery lined in black.
- ‘E’ 0-8-0 Locomotive class
- The Webb 4-cylinder class ‘B’ compound goods engines suffered with excessive weight on their leading wheels and, in an attempt to reduce this, 26 were modified from 1904 to have a leading pony truck. From 1911 these became known as class ‘E’.
- Eight-Coupled Locomotive
- A locomotive with eight driving wheels coupled together, usually 0-8-0 or 2-8-0 wheel arrangement.
- Experiment Locomotive Class (1)
- A series of 30 three cylinder compounds built in the 1880’s, the first of Webb’s compounds apart from a few experimental engines. The name might be thought to have a scientific connection, as with “Problem” and “Theorem”. This class, however, was Webb’s large-scale experiment with a class of express compound locomotives, and the first engine was named accordingly.
- Experiment 4-6-0 Locomotive Class (2)
- Built from 1905, these were a class of 105 two cylinder simple 4-6-0’s built by George Whale. Unlike the Webb “Experiments” there was nothing experimental about the class, which was a 4-6-0 development of the Whale “Precursors”. The first engine simply inherited the name of the first Webb “Experiment” after that engine was scrapped.
- Extra Large Bloomer 2-2-2 Locomotive Class
- In 1861 McConnell produced three enlarged ‘Bloomers’ at Wolverton Works . They had 7ft 6in driving wheels and boilers with various McConnell patent features. See also Bloomer, Large Bloomer, and Small Bloomer
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