The designation OKl27 stands for a passenger (O) tank locomotive (K) with the wheel arrangement 2-6-2 (l), which was designed in 1927. They were the first locomotives designed and built entirely in Poland and a total of 122 were built between 1928 and 1933. In terms of appearance, they were reminiscent of typical German steam locomotives, just when you look at the driver's cab with the bent side walls. They were delivered by H. Ceglielski from Posen.

Thanks to its symmetrical axle arrangement, it was equally suitable for fast driving in both directions, which made it suitable for the use on suburban railways. When it was introduced, it was the heaviest 2-6-2 tank locomotive in Europe and the maximum axle load was around 18 tonnes.

With good coal, the locomotives were able to pull a passenger train weighing 350 tonnes at 80 km/h on level ground, on a gradient of 1.4 percent this was still 60 km/h with 130 tonnes. Although the running characteristics became a bit unsteady from 50 km/h, this hardly disturbed the operation on suburban trains with many stops. After the invasion from the Germans, 120 of the locomotives were operated by the Reichsbahn as class 75¹². After the end of the war still 95 engines remained in Poland, which were used by the PKP in the areas around Warsaw and Katowice. After retirement from passenger train service, some were sold to private railways. Today four pieces are preserved, half of which are set up as monuments and half in museums.

After the Second World War, the PKP had the Pt47 developed as a further development of the pre-war Pt31. The P stood for passenger train, the t for the wheel arrangement 2-8-2 and the number for the year of development. In the basic dimensions they corresponded to their predecessor. 120 locomotives were built by Fablok and 60 by Cegielski.

The main changes to the boiler were in the firebox. This was now made of steel and had three brick arches to increase the heating area. In addition, the sand box and the steam dome were under a common panel, which additionally dried the sand. The leading axle was still in a Krauss-Helmholtz bogie together with the first coupled axle, while the trailing axle was a simple Adams axle.

The tenders were initially taken from the German classes 41 and 44. Later engines received new Polish tenders with a significantly increased coal capacity of 17 tonnes. The water tank initially held 33 cubic meters and was later reduced to 27 cubic meters by installing a mechanical stoker.

The Pt47 could reach 110 km/h, but could not quite keep up with Pacifics when it came to smooth running. But a larger starting tractive effort was available and the top speed could be reached with trains of up to 600 tonnes. Thanks to their power, they were able to stay in service well into the 1980s. From a total of 15 preserved machines, only one is operational today.