Class T 9.1 of the Prussian state railways were goods train tank locomotives with a 0-6-2T wheel arrangement.

[3] Several examples of this engine were handed over to foreign railway administrations and some of them later returned to the Deutsche Reichsbahn fleet during the Second World War as 90 246 - 251.

The T 9 Elberfeld variant of the Prussian state railways was a goods train tank locomotive with an 0-6-2 wheel arrangement.

For that purpose the firm of George Krauss built four examples, which were very similar to the Bavarian D VIII, because the Prussian T 3 was deemed to be too underpowered.

They were planned for service on the Aartalbahn between Wiesbaden and Langenschwalbach (today Bad Schwalbach), because this line, with inclines of up to 3,3%, had proven too steep for the Prussian T 3 engines on duty there.

In 1930, following the takeover of the Bremen harbour railway, two more locomotives of this type joined the Deutsche Reichsbahn as numbers 90 232 and 90 233.

The single Upper Hessian Railway variant of the T9 was a goods train tank locomotive with a 0-6-2T wheel arrangement.

Class T 9.2 of the Prussian state railways were goods train tank locomotives with a 2-6-0T wheel arrangement.

Of the 235 machines built, 154 units were incorporated by the Deutsche Reichsbahn in its 1923 renumbering plan and designated as DRG Class 91.0-1.

The Reichsbahn engine, 91 134, has been preserved and since August 2006 has been owned by the Mecklenburg Railway Society (Mecklenburgische Eisenbahnfreunden) in Schwerin.

Class T 9.3 of the Prussian state railways were tank locomotives that were used both in passenger and freight train services.

This was an evolutionary development of the Prussian T 9.2, in which the main difference was the use of a Krauss-Helmholtz bogie instead of an Adams axle.

On 1 April 1949,[12] the Deutsche Reichsbahn (GDR) took over yet more T 9.3s from private railway companies, with the numbers 91 6501, 6576, 6577, 6581 and 6582, some of which had been converted to superheating.