Parallel to the T 11, the T 12 was developed using superheated steam technology in order to achieve greater power with higher production costs. Despite the fact that both machines were initially produced in parallel, the advantages of the T 12 ultimately outweighed the costs, which is why it was the only one that continued to be built from 1910 onwards. The starting point in the development were four locomotives, which were manufactured in 1902 with a smoke box superheater. Series production of this variant did not follow, but in 1905 production began of a variant with the Schmidt-type smoke tube superheater, which had become established.

In order to achieve good acceleration for suburban traffic, the cylinders were dimensioned relatively large compared to the boiler. This resulted in the peculiarity in operation that they could accelerate very quickly to a high speed between the stops, but by this time the boiler reserve had already been used up. The latter was quickly refilled at the following stop to allow rapid acceleration again. If these locomotives had also been used over longer distances, only part of the available power could have been used.

74 1230 in September 2010 in the Berlin-Schöneweide depot

Wassen

As with the T 11, the leading axle was designed as a Krauss-Helmholtz bogie together with the first coupled axle, in order to enable smooth running on brisk runs with constantly changing speeds. Here, too, the cylinders were arranged relatively far back, which led to long, visible intake pipes and improved smooth running under load.

The locomotives built after 1913 were recognizable by a Knorr surface preheater, which was located behind the steam dome on the top of the boiler. Although the frame was also used as a water tank, the T 12's water supply was comparatively modest. However, this did not turn out to be a disadvantage, as there were enough opportunities to catch water on the Berlin suburban railways. Production lasted until 1921, since only then was a sufficient number available. Of the 1,014 locomotives, 25 also went to the Reichseisenbahnen Alsace-Lorraine and a few more to the Halberstadt-Blankenburg Railway and the Lübeck-Büchen Railway. The latter received a further eleven units in 1938, five of which were also fitted with fairings in the style of the famous streamlined locomotives nos. 1-3.

At the Reichsbahn, the 899 remaining locomotives were given the numbers 74 401 to 74 543 and 74 545 to 74 1321. Since large parts of the Berlin suburban network were electrified in the second half of the 1920s, many of the engines were now used in shunting service or on short distances in front of passenger and freight trains, as they were not suitable for longer distances. After the Second World War, a larger number came to both German railway administrations and both had them phased out by 1968.