Baltimore and Ohio class S

S class and S-1 class
B&O S-1 class #6206 in 1928
Type and origin Power type Steam Builder Baldwin (S class) Baldwin and Lima (S-1 class) Build date 1914 (S class) 1923–1926 (S-1 class) Total produced 31 (S class) 125 (S-1 class)
Specifications Configuration: ​  • Whyte 2-10-2 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Driver dia. 58 in:1473 mm(S class) 64 in:1626 mm(S-1 class) Wheelbase:  • Engine 436.510 Ib(198.0 t : S-1 class) (184.16 : S Class)  • Drivers 347.230 Ib(157.5 t S-1 class) (152.77 t : S class) Boiler: ​  • Diameter 90 in to 100 in (2286 mm to 2540 mm : S-1 class) Boiler pressure 220 Ib:15.5 kg/cm2(S-1 class) 200 Ib:14.1 kg/cm2(S Class ) Heating surface 5270 sq.ft(489.6 m2 : S-1 class) (517.8 m2 : S class)  • Tubes 4881 sp.ft(140.5 m2 : S-1 class)  • Firebox 262 sq.ft(S-1 class) Superheater: ​  • Heating area 1512 sq.in(140.5 m2 : S-1 class) (123.5 m2 : S class) Cylinder size 30 in x 32 in (762 mm x 813 mm : S-1 class) 30 in x 32 in (762 mm x 813 mm : S class)
Career Operators Baltimore and Ohio Railroad Class S and S-1 Number in class 31 (S class) 125 (S-1 class) Numbers 6000–6030 (S class) 6100–6224 (S-1 class) Nicknames "big sixes" Locale Eastern United States

Baltimore and Ohio Class S comprised two classes of 2-10-2 locomotives.

The S class proper were 31 locomotives built in 1914 by Baldwin Locomotive Works and numbered 6000–6030. The S-1 class comprised 125 locomotives numbered 6100–6224. They were built between 1923 and 1926, 75 by Baldwin and 50 by Lima Locomotive Works (#6150–6199).

They were nicknamed "big sixes" because of their size and because, until renumbering in 1954, their road numbers all began with "6".