Prussian T 12

Updated: August 2026 – The Prussian T 12 is the superheated variant of the classic suburban locomotive: the same basic form as the older T 11, but with a superheater and therefore noticeably more powerful. This page shows you how to identify the class, what saturated and superheated steam mean in practice, and why both classes ended up in the same Reichsbahn class.

What is the Prussian T 12?

The Prussian T 12 is a tank locomotive with the 2’C wheel arrangement and a superheated boiler, built for suburban and local services on the Prussian State Railways. A two-axle bogie runs at the front, followed by three coupled driving axles; there is no separate tender.

It is the direct further development of the Prussian T 11, which implemented the same concept with saturated steam. Because the superheated variant ran more economically, it was procured in far greater numbers and shaped urban local services for decades – until electric multiple units took over the job. The Deutsche Reichsbahn grouped both classes together as Class 74. What operating one of these machines looked like is shown at the Bochum-Dahlhausen Railway Museum in a fully preserved locomotive depot.

Saturated steam, superheated steam, and what that means in practice

The difference between the T 11 and the T 12 is not a detail for engineers – it is the reason one class stayed small while the other became the standard.

Feature	T 11	T 12
Boiler type	Saturated steam, no superheater	Superheated, with superheater
Wheel arrangement	2’C	2’C
Type	Tank locomotive	Tank locomotive
Efficiency	Lower	Significantly better
Numbers built	Limited	Considerably larger
DRG class	Class 74, lower numbers	Class 74, higher numbers

A superheater heats the steam further after it leaves the boiler, before it reaches the cylinders. This keeps the steam dry, reduces condensation and makes the engine run more efficiently. In practice that means the same output with less coal and water – a decisive advantage in suburban services with constant starting and stopping. Boilers of this type are only built new in one place today, at the Meiningen Steam Locomotive Works, which also carries out major overhauls.

How to identify the class in the field

The general order for identifications like this – type first, then wheel arrangement, then markings – is explained in detail in the guide to identifying locomotive classes.

Where it fits into railway operations

Suburban services make demands that an express locomotive cannot meet and a shunting locomotive cannot meet either. The T 12 sits precisely in that gap:

• Frequent starts require sufficient tractive effort from a standstill – hence three coupled axles.
• Brisk running between stops requires a smooth ride – hence the leading bogie.
• Turnaround times without a turntable require a tank locomotive that runs just as well in reverse as forwards.
• Economical continuous operation requires a superheated boiler, because coal and water consumption add up significantly with dense diagrams.

Larger passenger-service tasks were handled by locomotives such as Class 78 with an additional trailing bogie, while branch-line and freight duties led to classes such as Class 93. The differences are directly readable in the wheel arrangement – a good example of how closely technology and operational role are linked.

Why the T 12 became the standard locomotive

It is rarely as clearly traceable in railway history as it is here that one technical variant almost completely displaced another. Three reasons come together.

Operation was costly. Suburban services mean constant starting and braking at high service intensity. Every saving in coal and water pays off immediately, because it adds up over hundreds of runs a day.

The superheater was mature. By the time the T 12 was procured, superheating technology had already proven itself. The initial extra cost for components and maintenance was clearly outweighed by the fuel saving.

The basic concept was already right. The wheel arrangement, type and dimensions of the T 11 suited the job. There was no need to design something new, only to swap the boiler technology – a development step with low risk and high benefit.

For observers this means: if you are standing in front of one of these machines in a museum, you are more likely to be looking at a T 12 than a T 11 – simply because there were far more of them. That is exactly why the number on the locomotive matters so much: the visible differences between the two classes are small, but the statistical expectation is clear. Anyone judging by eye alone is particularly likely to get this pair wrong.

Where you can see these locomotives today

Locomotives of this generation survive only in museums. The search accordingly works differently than for regular service:

• Research museum holdings: which locomotives exist, and which are operational?
• Wait for events and seasonal dates – for much of the time, locomotives stay in the shed.
• Follow community reports, because short-notice changes turn up there first.
• Note the condition: a locomotive can move from display to overhaul between two visits.

For photography, a straight side view pays off with these locomotives, because only there does the full wheel arrangement become visible. Light, smoke and shutter speed are covered by the guide Photographing steam trains; how to keep your finds usable long-term is shown in the article on keeping a sighting log.

Common mix-ups

Conclusion

The Prussian T 12 is the standard locomotive of steam-hauled suburban services: tank locomotive, 2’C wheel arrangement, superheated boiler. It differs from the T 11 not in concept but in boiler technology – and that is exactly what made it the most-built variant. The Reichsbahn grouped both into Class 74 and distinguished them by running number. Today you only encounter it in museums, where a close look at the wheel arrangement and markings pays off.