The first trial trips occurred on June 15, 1903, using a specially-built experimental locomotive.

This was an experimental locomotive which proved to be more powerful than the railway's requirements and also too heavy for much of its infrastructure.

Like many experimental locomotives, the K5 was only a qualified success.

It was therefore decided to order only one experimental locomotive from Dübs and Company.

There were also some one-off and experimental 4-6-4 locomotives.

Russia built three large experimental locomotives between 1939 and 1949.

Number 4009 was at one time used as an experimental spark-arresting locomotive, nicknamed "Renoster".

In 1952 the experimental diesel-mechanical locomotive, the Fell diesel, went into service.

As many other experimental locomotives showed, the theoretical benefits of high steam pressure were hard to realise in practice.

In 1950 it was modified to an experimental condensing locomotive.