LSWR M7 Class

LSWR/SR M7

National Railway Museum's M7 as preserved in LSWR livery.

Type and origin Power type Steam Designer Dugald Drummond Builder LSWR Nine Elms Works (95) LSWR Eastleigh Works (10) Build date 1897–1911 Total produced 105

Specifications Configuration: ​  • Whyte 0-4-4T Gauge 4 ft 8 1⁄2 in (1,435 mm) Driver dia. 67 in (1,702 mm) Trailing dia. 43 in (1,092 mm) Length 34 ft 8 in (10.57 m) Loco weight 60 long tons 4 cwt (134,800 lb or 61.2 t) Fuel type Coal Fuel capacity 3 long tons 5 cwt (7,300 lb or 3.3 t) Water cap 1,300 imp gal (5,900 l; 1,600 US gal) Boiler pressure 175 lbf/in2 (1.21 MPa) Cylinders Two, inside Cylinder size 18.5 in × 26 in (470 mm × 660 mm)

Performance figures Tractive effort 19,750 lbf (87.85 kN)

Career Operators London and South Western Railway, Southern Railway, Southern Region of British Railways Class M7 Power class LSWR / SR: K BR: 2P Locale Great Britain Withdrawn 1937 (1), 1948 (1), 1957–1965 Preserved Nos. 245 and 53 Disposition Two preserved, remainder scrapped

The LSWR M7 class is a class of 0-4-4 passenger tank locomotive built between 1897 and 1911. The class was designed by Dugald Drummond for use on the intensive London network of the London and South Western Railway (LSWR), and performed well in such tasks. Because of their utility, 105 were built and the class went through several modifications over five production batches. For this reason there were detail variations such as frame length. Many of the class were fitted with push-pull operation gear that enabled efficient use on branch line duties without the need to change to the other end of its train at the end of a journey.

Under LSWR and Southern Railway ownership they had been successful suburban passenger engines, although with the increased availability of newer, standard designs, many of the class were diagrammed to take on a new role as reliable branch line engines, especially in Southern England.

Members of the class lasted in service until 1964, and two examples have survived into preservation: number 245 in the National Railway Museum, and 53 (as BR 30053) on the Swanage Railway.

Drummond designed these locomotives to answer the need for a larger and more powerful version of William Adams' 0-4-4 T1 class of 1888. The Adams T1 design of 1888 with 5 ft 7 in (1,702 mm) wheels had been developed to meet the LSWR's requirement for a compact and sure-footed suburban passenger locomotive to be utilised on the intensive commuter timetables around London. However, by the mid-1890s the suburban services around London were growing at a rate which began to preclude the use of these and other older classes of locomotive.

The M7 tank locomotive was the first design by Dugald Drummond upon replacing William Adams as Locomotive Superintendent of the LSWR in 1895. It was an enlargement of the T1 with a sloping grate of increased area giving greater power. Drummond drew upon his previous experience with the successful London Brighton and South Coast Railway D1 class, whilst he was works manager at Brighton in the early 1870s, and his own 157 class of 1877, on the North British Railway in Scotland. It was the heaviest 0-4-4 type ever to run in Britain.