Midland Railway 483 Class

The Midland Railway 483 Class 4-4-0 was a class of steam-driven locomotive designed by Henry Fowler for passenger work on the Midland Railway. The class were nominally "rebuilds" of various earlier classes designed by Samuel W. Johnson, although the '483' class engines were, unquestionably, 'accountancy rebuilds' (effectively new locos 'disguised' to gain routine expenditure approval from the board). This design formed the basis for the later LMS Class 2P 4-4-0.

Construction of the first batch of this class was authorised by Midland Railway Order O/3942 dated 21 June 1911: 'Please put your work in hand in connection with rebuilding engines 483–522 with new frames, new cylinders and G7 boilers fitted with Schmidt's superheaters.' Apart from the savings made by using the parts that were salvaged from the old engines, there was an added benefit in referring to them as rebuilt since the royalties due to the superheater company were lower for modified locomotives than for new ones. This first batch of locomotives previously formed the 150 class. Their rebuilding to Class 483 took place 1912-1913.

Four more batches of rebuilds were authorised; in 1912, 1913, 1914 and 1922. The London, Midland and Scottish Railway (LMS) inherited these locomotives at the Grouping of the railways in 1923, completing the last of these rebuilds in 1924.

Some of them duly passed into British Railways (BR) ownership in 1948.

Numbering

 * BR numbers 40332-40397 (17 locomotives) originally built 1882–1891, some rebuilt from 1910 onwards
 * BR numbers 40400-40562 (143 locomotives) originally built 1891–1901, all rebuilt between 1912 and 1923
 * BR numbers 40322-40326 (5 locomotives) built for Somerset and Dorset Joint Railway 1914-1921 and taken into LMS stock in 1930

Note: two of the above number series contain gaps so the totals do not tally.

Rebuilding
On rebuilding, the Stephenson valve gear was retained but the following changes were made:
 * 18 x cylinders with slide valves were replaced by 20.5 x cylinders with piston valves.
 * 6 ft driving wheels were replaced by 7 ft driving wheels.
 * A superheater was fitted.