Class 50.40

Updated: August 2026 – A steam locomotive whose chimney sits at the side instead of the centre: Class 50.40 is the most striking German steam class of the post-war era – and at the same time one of the shortest-lived. 31 locomotives were built as Franco-Crosti conversions of Class 50. This page explains what lies behind the unusual boiler, why the concept failed, and why you can only find these locomotives in photographs today.

What is Class 50.40?

Class 50.40 refers to 31 Class 50 locomotives that were converted with a Franco-Crosti preheater boiler. A prototype was built in 1954, with the remaining 30 following in 1958 and 1959. They carried running numbers 50 4001 to 50 4031 and kept the wheel arrangement and running gear of the original design: 1’E, two cylinders.

The goal was fuel savings. And it was achieved – around 22% less coal consumption compared with the base design. Even so, the project ended after just a few years: the additional boiler corroded so badly that repairs ate up the savings. All locomotives had been withdrawn by June 1967. Not a single one survives.

How a Franco-Crosti boiler works

The idea is easy to follow: in a normal steam locomotive, a large share of the energy used escapes unused through the chimney. The Franco-Crosti boiler recaptures part of it.

The catch lies in the physics: if you cool flue gases far enough, you fall below the dew point. Condensate forms, and combined with sulphur compounds from the coal it becomes aggressive. This is exactly what the design failed on in everyday service. The guide to identifying classes explains how to systematically classify design differences like this.

Classification: three paths from the same base design

Class 50 was the most-built German freight locomotive – and correspondingly often the starting point for conversions. The approaches in East and West differed fundamentally.

Variant	Railway administration	Approach	Number built	Outcome
Class 50	DRG, later DB and DR	Base design, 1’E h2	over 3,000	Standard until the end of steam traction
Class 50.35	Deutsche Reichsbahn	Conventional new-build boiler 50E	208	Success, many locomotives survive
Class 50.40	Deutsche Bundesbahn	Franco-Crosti preheater boiler	31	Abandoned by 1967, none survive
Class 52.80	Deutsche Reichsbahn	Reconstruction of the wartime Class 52	200	Still present in heritage operation today

The comparison is instructive: the conservative solution of the rebuilt Class 50.35 succeeded, while the more technically ambitious experiment failed. The base design, Class 50 itself, remained unchallenged in service, while the three-cylinder Class 44 continued to handle heavy-duty work.

Research instead of spotting: how to find material

There is nothing to photograph for this class – no surviving vehicle, no monument, no museum locomotive. What remains is archival work, and it pays off:

• Historical photo archives. Photographs from the 1950s and 1960s show the locomotives in service. Watch the captions: the side-mounted chimney is often the first thing mentioned.
• Historical sections of large railway forums. Contemporary witnesses gather operating experience and original photographs there. The overview on researching historical railways describes how to search there effectively.
• Railway museum collections. Even though no locomotive survives, drawings, components and operating documents sit in museum holdings such as that of the German Steam Locomotive Museum Neuenmarkt-Wirsberg and can be researched there.
• Build your own well-organised archive. Anyone collecting historical material needs a structure with sources and dates from early on. The article on building a photo archive for spotters offers a practical system that also applies to third-party material.

If you want to photograph the related, surviving classes, the usual rules apply there: on museum premises and at special workings, tracks and operational railway land are off-limits, and barriers and staff instructions are binding. The steam-specific technique – light, viewpoint, handling the exhaust plume – is covered in the guide how to photograph steam trains.

It is worth noting that the Franco-Crosti principle was not a purely German topic. It originated in Italy and was trialled there on several classes too. Anyone searching online for photographs will therefore regularly come across Italian locomotives with the same characteristic side-mounted chimney. For identification, that means the side-mounted stack proves the design, not the class. Only the running number, markings and vehicle outline decide whether a German 50.40 or a foreign locomotive is shown.

The class is also historically interesting as a marker in time. It emerged in a phase in which the Deutsche Bundesbahn was already switching to diesel and electric traction, but was still investing money in optimising steam traction. The fact that the project was abandoned after just a few years therefore had economic as well as technical reasons: for a form of traction that was being phased out anyway, an elaborate fix was no longer worthwhile.

Common mix-ups

Conclusion

Class 50.40 is one of the most instructive German steam classes: sound in technical thinking, measurably better in fuel consumption, yet a failure in everyday service. Its side-mounted chimney makes it unmistakable in any photograph. For spotters it remains a pure archive subject – only the base design remains to be experienced, still under steam today thanks to overhauls at the Dampflokwerk Meiningen.