The U series was originally a narrow-gauge steam locomotive of the k.k. Austrian State Railways (kkStB) for a track 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 acquired in large numbers by nearly all operators of narrow-gauge railway lines in Austria and were manufactured by several locomotive factories. The last example of the U series was built in 1922 for the StLB, long after more modern locomotive types had 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 at museums and tourist railways. Some examples have also been set up as locomotive monuments. The locomotive numbered 298.05 fits very well with the ÖBB narrow-gauge cars of the LILIPUT program, as it operated as U 25 or 298.05 not only in the Steyr Valley but also on other narrow-gauge railways in Austria. It is now back in operation as a museum locomotive in the Steyr Valley.