SR Merchant Navy Class

SR Merchant Navy class

Official Southern Railway photograph of 21C1 Channel Packet as built, 1941

Type and origin Power type Steam Designer Oliver Bulleid Builder SR Eastleigh Works Build date 1941–1949 Total produced 30

Specifications Configuration 4-6-2 (Pacific) Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 1 in (0.940 m) Driver dia. 6 ft 2 in (1.880 m) Trailing dia. 3 ft 7 in (1.092 m) Length 69 ft 8 in (21.23 m) Loco weight 94.75 long tons (96.3 t; 106.1 short tons) Fuel type Coal Fuel capacity 5.00 long tons (5.1 t; 5.6 short tons) Water cap 5,000 imp gal (22,730 L; 6,000 US gal) Firebox:  • Firegrate area 48.5 sq ft (4.51 m2) Boiler pressure 280 psi (19.31 bar; 1.93 MPa), later reduced to 250 psi (17.24 bar; 1.72 MPa) Cylinders 3 Cylinder size 18 in × 24 in (457 mm × 610 mm)

Performance figures Tractive effort 37,515 lbf (166.9 kN)

Career Operators Southern Railway → British Railways (Southern Region) Class SR / BR: Merchant Navy Power class SR: A BR: 8P Locale Great Britain Disposition All modified (see below)

BR Modified Merchant Navy class

35028 "Clan Line" as modified without the air-smoothed casing and with Walschaert's valve gear

Type and origin Power type Steam Designer R. G. Jarvis after Oliver Bulleid Rebuilder Eastleigh Works Rebuild date 1956–1960 Number rebuilt 30

Specifications Configuration 4-6-2 (Pacific) Gauge 4 ft 8 1⁄2 in (1,435 mm) Leading dia. 3 ft 1 in (0.940 m) Driver dia. 6 ft 2 in (1.880 m) Trailing dia. 3 ft 7 in (1.092 m) Length 71 ft 7 in (21.82 m) Loco weight 97.90 long tons (99.5 t) Fuel type Coal Fuel capacity 5 long tons (5.1 t) Water cap 6,000 imp gal (27,280 L; 7,210 US gal) Firebox:  • Firegrate area 48.5 sq ft (4.51 m2) Boiler pressure 250 psi (1.72 MPa) Cylinders 3 Cylinder size 18 in × 24 in (457 mm × 610 mm)

Performance figures Tractive effort 33,495 lbf (149.0 kN)

Career Operators Southern Region of British Railways Class Merchant Navy Power class 8P Locale Great Britain Withdrawn 1964–1967 Disposition 1 sectioned, 10 preserved, remainder scrapped

The SR Merchant Navy class (originally known as the 21C1 class, and later informally known as Bulleid Pacifics, Spam Cans or Packets) is a class of air-smoothed 4-6-2 Pacific steam locomotives designed for the Southern Railway by Oliver Bulleid. The Pacific design was chosen in preference to several others proposed by Bulleid. The first members of the class were constructed during the Second World War, and the last of the 30 locomotives in 1949.

Incorporating a number of new developments in British steam locomotive technology, the design of the Merchant Navy class was among the first to use welding in the construction process; this enabled easier fabrication of components during the austerity of the war and post-war economies. In addition the locomotives featured thermic syphons in their boilers and the controversial Bulleid chain-driven valve gear. The class members were named after the Merchant Navy shipping lines involved in the Battle of the Atlantic, and latterly those which used Southampton Docks, a publicity masterstroke by the Southern Railway, which operated Southampton Docks during the period.

Due to problems with some of the more novel features of Bulleid's design, all members of the class were modified by British Railways during the late 1950s, losing their air-smoothed casings in the process. The Merchant Navy class operated until the end of Southern steam in July 1967. A third of the class has survived and can be seen on heritage railways throughout Great Britain.

The Southern Railway was the most financially successful of the "Big Four", but this was largely based on investment in suburban and main line electrification . After the successful introduction of the SR Schools class in 1930, the railway had lagged behind the others in terms of modernising its ageing fleet of steam locomotives. Following the retirement of the General Manager of the Southern Railway Sir Herbert Walker and Richard Maunsell the Chief Mechanical Engineer (CME) in 1937, their successors considered that the time had come to change this situation. In March 1938, the new General Manager Gilbert Szlumper authorised Oliver Bulleid, Maunsell's replacement, to prepare designs for twenty express passenger locomotives. The deteriorating international situation prior to the Second World War was an additional factor in this decision.