When the Pfalzbahn wanted to try out new ways of temporarily increasing the tractive effort of express locomotives, they ordered a locomotive from Krauss that was called “Dr. von Clemm”. Here a Helmholtz patent was used, which Kraus had already used on the Bavarian AA I and which provided for an additional, lowerable axle with an additional steam engine. While the basic construction of the AA I corresponded to the wheel arrangement 4-2-2 and there the additional axle was installed in front of the coupled axle in the frame, the P 3^II was a 4-4-2 (Atlantic), in which the additional axle was placed in the middle of the bogie. 

Again, it was a flangeless axle with smaller wheels that was lifted by spring power when not in use and could be lowered onto the rails by steam pressure when needed. The booster unit was designed as a simple engine with a cylinder size of 260 by 400 mm, while the main power plant had two compound-acting cylinders, which were placed on the inside of the frame for space reasons. Another innovation were balancing weights, which were installed under covers between the second coupling and the trailing axis on both sides next to the ash pan. These were driven by additional coupling rods and were intended to improve smooth running at high speeds.

Since the innovations of the P 3^II looked groundbreaking on paper, the locomotive was awarded a Grand Prix at the Paris Exhibition in 1900. In practice, it quickly became apparent that the additional engine was unreliable and its benefits did not justify the increased maintenance effort. In addition, the load on the first bogie axle was increased to over 14 tonnes when the driving axle was raised, which was more than with the coupled axles. Even the balancing weights, with their additional complexity, could not quite meet the expectations placed in them.

So it was as early as 1902 that the additional axle, together with the cylinders and the counterweights, were removed. Due to the weight of the front cylinders being eliminated, the axle load of the first axle was now kept within limits. The Bavarian AA I met the same fate a few years later. The P 3^II was now the most powerful Atlantic express locomotive in Germany with a calculated output of between 1,100 and 1,200 hp. It was now used like other Atlantic locomotives and was still in use in the early 1920s, which is why it was assigned the Reichsbahn number 14 121. However, this number was not actually written onto he locomotive, since the decommissioning took place in 1924.