The Prussian S 9 was an express
steam locomotive
A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...
with the
Prussian state railways
The term Prussian state railways (German: ''Preußische Staatseisenbahnen'') encompasses those railway organisations that were owned or managed by the State of Prussia. The words "state railways" are not capitalized because Prussia did not have a ...
, first built in 1908. It had a
4-4-2 (''Atlantic'')
wheel arrangement
In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and ...
and a four-
cylinder
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infi ...
compound engine
A compound engine is an engine that has more than one stage for recovering energy from the same working fluid, with the exhaust from the first stage passing through the second stage, and in some cases then on to another subsequent stage or even s ...
. It was developed by the firm of
Hanomag
Hanomag (Hannoversche Maschinenbau AG, ) was a German producer of steam locomotives, tractors, trucks and military vehicles in Hanover. Hanomag first achieved international fame by delivering numerous steam locomotives to Grand Duchy of Finland ...
in
Hanover
Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German state of Lower Saxony. Its 535,932 (2021) inhabitants make it the 13th-largest city in Germany as well as the fourth-largest city in Northern Germany ...
who delivered a total of 99 engines of this class.
There were also some high-speed trials locomotives which were classified as S 9s, but did not belong to this particular class. These included two cab-forward 4-4-4 locomotives Altona 561 and 562.
Although at the time
superheated technology was widespread, the state of
Prussia
Prussia, , Old Prussian: ''Prūsa'' or ''Prūsija'' was a German state on the southeast coast of the Ba