The London, Midland and Scottish Railway and British Railways Class 4 2-6-4T was a family of classes of steam locomotives. A grand total of 800 engines were built to five separate designs by four different mechanical engineers, over a period of 29 years. Each new design was a development of the previous one. The LMS gave the whole family the power classification 4P, BR 4MT. It is therefore worth considering them as a group as follows:
| LMS Nos | BR Nos | Design | Designer | Built | Built by LMS | Built by BR | Total built | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2300–2424 | 42300–42424 | 1927–1934 | align=right | 125 | align=right | 0 | align=right | 125 | |||
| 2500–2536 | 42500–42536 | 1934 | align=right | 37 | align=right | 0 | align=right | 37 | |||
| 2425–2494, 2537–2672 | 42425–42494, 42537–42672 | 1935–1943 | align=right | 206 | align=right | 0 | align=right | 206 | |||
| 2187–2299, 2673–2699 | 42050–42299, 42673–42699 | 1945–1951 | align=right | 130 | align=right | 147 | align=right | 277 | |||
| — | 80000–80154 | 1951–1956 | align=right | 0 | align=right | 155 | align=right | 155 | |||
| Total | 1927–1956 | style=text-align:right | 498 ! | style=text-align:right | 302 ! | style=text-align:right | 800 |
All engines were withdrawn from stock between 1959 and 1967, summarised as follows:
| 1959 | 5 | 0 | 0 | 0 | 0 | 5 | |||||||
| 1960 | 11 | 1 | 2 | 0 | 0 | 14 | |||||||
| 1961 | 22 | 7 | 17 | 3 | 0 | 49 | |||||||
| 1962 | 37 | 29 | 43 | 43 | 1 | 153 | |||||||
| 1963 | 16 | 0 | 29 | 30 | 0 | 75 | |||||||
| 1964 | 20 | 0 | 51 | 57 | 31 | 159 | |||||||
| 1965 | 12 | 0 | 38 | 54 | 44 | 148 | |||||||
| 1966 | 2 | 0 | 11 | 48 | 54 | 115 | |||||||
| 1967 | 0 | 0 | 15 | 42 | 25 | 82 | |||||||
| Total | style=text-align:right | 125 ! | style=text-align:right | 37 ! | style=text-align:right | 206 ! | style=text-align:right | 277 ! | style=text-align:right | 155 ! | style=text-align:right | 800 |
|---|
| 1958 | 125 | 37 | 206 | 277 | 155 | 800 | |
| 1959 | 120 | 37 | 206 | 277 | 155 | 795 | |
| 1960 | 109 | 36 | 204 | 277 | 155 | 781 | |
| 1961 | 87 | 29 | 187 | 274 | 155 | 732 | |
| 1962 | 50 | 0 | 144 | 231 | 154 | 579 | |
| 1963 | 34 | 0 | 115 | 201 | 154 | 504 | |
| 1964 | 14 | 0 | 64 | 144 | 123 | 345 | |
| 1965 | 2 | 0 | 26 | 90 | 79 | 197 | |
| 1966 | 0 | 0 | 15 | 42 | 25 | 82 | |
| 1967 | 0 | 0 | 0 | 0 | 0 | 0 |
For technical purposes, it is worth splitting the Fairburn tanks into two subclasses; early (42050–42146) and late (42147–42699) as their weights differ slightly.
| Attribute | Fowler | Stanier, 3 cylinder | Stanier, 2 cylinder | Fairburn (early)[1] | Fairburn (late)[2] | BR Standard | |
|---|---|---|---|---|---|---|---|
| Leading wheel diameter | 3feet | 3feet | |||||
| Driving wheel diameter | 5feet | 5feet | |||||
| Trailing wheel diameter | 3feet | 3feet | |||||
| Wheelbase | 38feet | 37feet | 36feet | ||||
| Length | 47feet | 45feet | 44feet | ||||
| Weight | 86.252NaN2 | 92.252NaN2 | 87.752NaN2 | 85.252NaN2 | 84.72NaN2 | 86.52NaN2 | |
| Axleload | 17.952NaN2 | ||||||
| Coal capacity | 3.52NaN2 | ||||||
| Water capacity | 2000-2NaN-2 | 1875-2NaN-2 | 2000-2NaN-2 | ||||
| Boiler | G8AS | 4C | ABR5 | ||||
| Boiler pressure | 2002NaN2 | 2002NaN2 | 2252NaN2 | ||||
| Firegrate area | 25square feet | 25square feet | 26.7square feet | ||||
| Heating surface: Tubes | 1082square feet | 1011square feet | 1223square feet | ||||
| Heating surface: Firebox | 138square feet | 137square feet | 143square feet | ||||
| Superheater area | 266 sq ft / 246 sq ft | 160 sq ft/154 sq ft | 240square feet | ||||
| Cylinders | 2 outside | 3 (1 inside, 2 outside) | 2 outside | 2 outside | 2 outside | 2 outside | |
| Cylinder size | 19x | 16x | 19.625x | 18x | |||
| Tractive effort | 231252NaN2 | 245982NaN2 | 246712NaN2 | 255152NaN2 | |||