The U series was originally a narrow-gauge steam locomotive of the k.k. Austrian State Railways (kkStB) for a gauge of 760 mm. It is one of the most widely built narrow-gauge locomotives in Europe. The locomotives proved to be so reliable that they were procured in large numbers by nearly all operators of narrow-gauge railway lines in Austria and were built by several locomotive manufacturers. The last specimen of the U series was constructed as late as 1922 for the StLB, at a time when much more modern locomotive types already existed. Those U series locomotives that passed into the possession of the ÖBB after World War II were designated as series 298 with two-digit order numbers starting in 1953. Due to their large numbers, many machines of this type are still operational today in museums and tourist railways. Some specimens have also been erected as locomotive monuments. The locomotive numbered 298.05 pairs very well with the ÖBB narrow-gauge cars from the LILIPUT program, as it operated not only in the Steyr Valley as U 25 or 298.05 but also on other narrow-gauge railways in Austria. It now runs again as a museum locomotive in the Steyr Valley.