In real life the first steam locomotive to operate on rails was built in 1804 (1807 - first passenger service). Diesel and electric trains and locomotives replaced steam engines in many countries in the decades after World War II.
In game first temperate climate railway train (Kirby Paul Tank) is available in 1925. The first sub-arctic and tropical landscapes train (Wills 2-8-0) is available in 1945. And the first toyland train is available in 1946.
These default tracks support Diesel and Steam powered vehicles, but will not allow the running of Electric trains (unless Electrified Rails patch is disabled).
There are the 4 Steam trains available in Temperate climate:
As well as 6 Diesel trains available in Temperate climate:
There is 1 Steam train available in Sub-arctic and Tropical climates:
As wells as 7 Diesel trains available in Sub-arctic and Tropical climates:
There are 3 Steam trains available in Toyland landscape:
As well as 2 Diesel trains available in Toyland landscape: