Class 78

Updated: August 2026 – A steam locomotive that ran backwards just as fast as forwards: that was the real trick of the Class 78. Behind the number stands the Prussian T 18, a large passenger tank locomotive with the wheel arrangement 2’C2’, rated for 100 km/h in both directions. Today it’s a historic vehicle – and in museum operation one of the most impressive tank locomotives of all.

What is the Class 78?

The Class 78 is the Reichsbahn designation for the Prussian passenger tank locomotive of the T 18 class, procured from 1912. It carries the wheel arrangement 2’C2’: a two-axle bogie at the front, three coupled driving axles in the middle, a two-axle carrying bogie at the rear. It’s rated for 100 km/h, in both directions of travel.

That made it an exceptional vehicle for its time: fast enough for high-quality passenger trains, but without a separate tender and therefore without turning manoeuvres at the terminus. Today the Class 78 is no longer in regular service; surviving engines belong to museums and societies.

Reading the Prussian class system

Before 1925, every Länderbahn had its own designation system. The Prussian one worked with a letter for the purpose and a number for the class. The wheel arrangement wasn’t directly apparent from it – unlike the Bavarian system with its fractions.

Class letter	Meaning	Well-known example
S	Express locomotive with separate tender	S 10
P	Passenger locomotive with separate tender	P 8, later Class 38
G	Freight locomotive with separate tender	G 8, G 10, G 12
T	Tank locomotive with no separate tender	T 12, T 18
Number after it	Class and power category	the higher, the larger

The T 18 was the largest of these tank locomotive classes. Smaller members of the same series include the Prussian T 12, and the best-known example for the letter P is the Class 38 with the Prussian P 8. From 1925, the Reichsbahn’s class scheme replaced all these systems and ordered vehicles by purpose, tank design and wheel arrangement.

How to identify a T 18

The general order for identifying vehicles is explained in the guide to identifying classes – it works for steam locomotives just as it does for modern powered vehicles, only with different features.

Classification within railway operations: why the 2’C2’ design was so practical

The operational core of the T 18 can be summed up in one sentence: it never had to be turned. With a classic tender locomotive like the Class 64 in branch-line service, running in reverse is possible but slow. Only two-axle carrying units at both ends guide the locomotive cleanly at speed even when it’s running cab-first.

That’s exactly what was needed in suburban and short-distance traffic: short turnaround times, tight diagrams, no turntable at every terminus. The T 18 was thus an early answer to a problem that the push-pull train with a driving trailer, and eventually the multiple unit, would go on to solve for good.

The price of this design is weight and length. Two additional carrying axles at each end support the boiler and supplies, but deliver no tractive effort. A T 18 is therefore, relative to its size, not a particularly powerful machine – it was optimised for speed and reversibility, not heavy loads. That’s precisely the difference between a passenger and a freight locomotive, made visible in the running gear.

For photographers at museum operations, this brings a peculiarity: unlike with most steam locomotives, a cab-first shot here isn’t a compromise but the operationally intended normal case. Anyone who still wants the classic view checks the direction of travel of the train beforehand. How to choose viewpoint, light and timing for steam trains is covered in the guide how to photograph steam trains.

Spotting: how to get a 78 in front of your camera

Searching for a historic steam locomotive follows different logic to spotting modern vehicles. There’s no diagram you could look up – but there are dates that are fixed well in advance.

The starting point is heritage railways and railway museums with steam holdings such as the Darmstadt-Kranichstein Railway Museum: their vehicle lists tell you which machines even exist and in what condition. After that, check the supporting societies, because overhauls, boiler certificates from the Meiningen Steam Locomotive Works and returns to service are communicated there first. Finally, cross-check event calendars – steam festivals and anniversaries bring several machines together in one place and are especially rewarding for photographers.

How to reliably find such dates and what to consider when planning is described in detail in the guide to finding special trains and special workings. Expect delays as standard: special trains run according to path availability, not a clock-face timetable.

Common mix-ups

Conclusion

The Class 78 is the steam locomotive that best explains the principle of “built symmetrically, fast in both directions”. Two-axle units at front and rear, three coupled axles in between, 100 km/h in either direction: that made the Prussian T 18 one of the most practical passenger locomotives of its era. It no longer exists in regular service, but in museum operation it’s a vehicle well worth seeking out.