In the 1930s, the Reichsbahn had the goal of significantly accelerating freight traffic. The class 45 with a 2-10-2 wheel arrangement was developed as the most powerful freight locomotive among the standard locomotives in order to complete the classes 41 and 44 upwards. The requirements stipulated that 1,200 tonnes could be hauled at 80 km/h on the level and 1,000 tonnes at 60 km/h on a gradient of 0.5 percent. In addition, despite its many axles, the locomotive should also be able to negotiate the smallest curve radii, which was made possible by axles with lateral play and Krauss-Helmholz bogies.
Two pre-production locomotives were built in November 1936 and June 1937, but it was not until 1940 and 1941 that the 26 production locomotives with the numbers 45 003 to 45 028 were delivered, which were somewhat more powerful. They proved their high power right from the start and were not only used in express freight services, but also competed with the actual express locomotives such as the class 01 in express service.
Although they could not reach the same top speed, they were able to maintain a high speed with an indicated continuous output of around 3,000 hp (or 2,800 hp for the two pre-production locomotives) even on long inclines with a heavy express train. By overloading them for short time, it was even possible to calculate an output in the range of 3,500 hp. In addition, express locomotives often reached the limits of adhesion, which happened much less frequently with the five coupled axles of the 45. Finally, the class 01 and 03 locomotives with only two cylinders developed rough running characteristics under full steam, while the 45 with three cylinders ran much more smoothly. In addition, the axle load could be changed between 18 and 20 tonnes depending on the required adhesive weight and capacity of the lines traveled. To do this, only a few bolts on the chassis had to be repositioned, which changed the load on the carrying axles.
However, the inadequacies of the then widespread steel type St 47 K as a material for the boiler soon became apparent. As a result, the pressure soon had to be reduced from the targeted 20 to 16 bars. In addition, the long smoke tubes of the largest standard locomotives soon caused problems due to excessive stress. After all, such a powerful locomotive required a lot of coal, which is why two firemen always had to be used due to the lack of an automatic stoker. Ultimately, plans for the procurement of about 100 more units were dropped, since the war was already raging and the less powerful but much cheaper war locomotives were preferred. In addition, the maintenance of a rail network meant too much effort for the high axle load of 20 tonnes in these times.
After the war, only one remained with the Reichsbahn, which was tested with a forced circulation boiler, condensation tender and pulverized coal firing without success. In contrast, the locomotives which were refurbished by the Bundesbahn received new, welded boilers and some had a stoker, so they remained in use for a longer period of time. When they were given computer numbers in 1968, there were still three which were used as brake locomotives.
