LSWR X6 class
No. 666 was built 1892, withdrawn 1943 and dumped at Eastleigh - 11 July 1946
Type and origin Power type Steam Designer William Adams Builder LSWR Nine Elms Works Build date 1895–1896 Total produced 10
Specifications Configuration: ​  • Whyte 4-4-0  • UIC 2′B n2 Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 3 ft 7 in (1.092 m) Driver dia. 6 ft 7 in (2.007 m) Length 54 ft 5+3⁄8 in (16.60 m) Height 13 ft 2+3⁄4 in (4.03 m) Fuel type Coal Boiler pressure 175 psi (1.21 MPa) Cylinders Two, outside Cylinder size 19 in × 26 in (483 mm × 660 mm)
Performance figures Tractive effort 17,673 lbf (78.6 kN)
Career Operators LSWR · Southern Railway Class X6 Power class SR: I Withdrawn 1933–1946 Disposition All scrapped

The LSWR X6 class was a class of express passenger 4-4-0 steam locomotives designed for the London and South Western Railway by William Adams. Ten were constructed at Nine Elms Locomotive Works between 1895 and 1896.

The class were numbered 657–666, and just as the T3 class were a smaller-wheeled version of the X2 class, the X6 class were a smaller-wheeled version of the T6 class. The boiler was identical to that used the T6 class.^[1] Some of the engines were subsequently fitted with a Drummond boiler, including No. 658 which was the last Adams 4-4-0 to remain in service.^[2]

All passed to the Southern Railway at the grouping in 1923. Withdrawals started in 1933, and by the start of World War II, only six remained. Five were retired during the war, leaving only No. 658, which was withdrawn in December 1946. All were scrapped.