Sächsische Dampfeisenbahngesellschaft mbH (SDG)

Updated: August 2026 – Only a few rail operators carry their traction type in their company name. The Sächsische Dampfeisenbahngesellschaft mbH does – and in doing so names exactly what made Saxon narrow gauge famous the world over. This page shows you how to tell the design families of these locomotives apart in the field, without having to read a single number.

What is Sächsische Dampfeisenbahngesellschaft mbH?

Sächsische Dampfeisenbahngesellschaft mbH (SDG) is a narrow-gauge railway operation in the legal form of a GmbH. The company name names three things: the state reference, the defining traction type, and the legal form. It names neither a line nor a fleet – both are deliberately left off this page.

Saxon narrow gauge means 750 mm gauge against 1,435 mm on the standard network. Almost everything else follows from this measurement: tighter curves, smaller vehicles, lower axle loads – and its own, clearly defined world of locomotives, such as can be seen on the Fichtelbergbahn in the Ore Mountains.

Design families: the quickest way to sort them in your head

Saxon narrow-gauge steam locomotives look similar in photos at first glance. In fact, they can be sorted with just a few questions – and these questions work on any line and in any era.

Question	Possible answers	What follows from it
Tank or tender locomotive?	Supplies on the vehicle, or a separate tender	Narrow-gauge locomotives almost always carry their own supplies
How many sets of running gear?	one, or two separate	Two sets of running gear mean a double-jointed design for tight curves
How many coupled axles?	two to five	More coupled axles mean more adhesive weight
Any leading/trailing axles?	front, rear, none	Leading/trailing axles improve the curve-running of faster machines
Where are the water tanks?	on the side of the boiler, or under the cab	Shapes the silhouette and visually separates the design groups

The second row is the real key. A locomotive with two separate sets of running gear, movable relative to each other, under a single boiler is a double-jointed design. It was developed specifically to negotiate very tight curves, and it’s the characteristic feature of the older Saxon narrow-gauge machines. Spot two cylinder groups, and you no longer need the number.

Later designs took a different path: a continuous frame, more coupled axles, a bigger boiler. These machines look longer and more substantial, run more smoothly and pull more – but in return demand more generous curve radii.

Recognition in the field

The general system behind this is explained in the guide to identifying classes; how to keep the result usable long-term is shown in the guide to reporting sightings.

Standard gauge for comparison – and the diesel side

The quickest way to get an eye for narrow-gauge scale is through comparison. Standard-gauge tank locomotives such as the Class 89 or the heavy Class 94 follow the same design principle – supplies carried on the vehicle, no separate tender – but look noticeably bulkier alongside.

Besides steam operation, every narrow-gauge network also has a diesel side for shunting and secondary tasks, such as small diesel locomotives of the LKM Ns 2 type. Such vehicles rarely take the spotlight, but they’re indispensable for operations. You’ll find the same small-locomotive families at the even narrower field-railway scale, for instance at the Historische Feldbahn Dresden.

How the same vehicle world looks at neighbouring operations is shown by pages such as the Sächsisch-Oberlausitzer Eisenbahngesellschaft, the Döllnitzbahn and the Eisenbahn-Bau- und Betriebsgesellschaft Pressnitztalbahn.

Safety during steam operation

Why knowing the designs is more useful than any fleet list

Fleet lists go out of date. Vehicles go in for maintenance, come back from overhaul, get loaned out or withdrawn. A list that’s correct today can be wrong in several lines within two years – and anyone who copies it unchecked passes the errors on.

Design knowledge, by contrast, doesn’t go out of date. A locomotive’s wheel arrangement doesn’t change, nor does the layout of its running gear, and its silhouette stays recognisable for decades. Once you can read these features reliably, you can place any photo, no matter what year it’s from or who owns the machine at the time.

In practice, that means: note not just the number at every sighting, but also the features that led you to it. Two cylinder groups, three coupled axles per running gear, side-mounted water tanks – such details can be checked later. A number alone can’t, if it’s blurred in the photo.

There’s a further advantage: design features work even where markings are missing. Especially on historic vehicles, markings are sometimes small, partly painted over, or not fitted at all. The builder’s plate and the design are then the only reliable clues left – and they’re what distinguishes a sighting from a mere memory.

It also pays to adopt a fixed order when photographing: first an overall side view of the locomotive, then the running gear, then the plates. Stick to that, and you’ll always end up with the images that support an identification – not just the pretty three-quarter view where the cylinders happen to be hidden. Two extra shots cost nothing and can save the whole identification if in doubt.

Common mix-ups

• Confusing a double-jointed locomotive with double-heading – two sets of running gear under one boiler are one locomotive, not two.
• Equating 750 mm with metre gauge – similar in photos, incompatible in operation – the Harzer Schmalspurbahnen run on metre gauge.
• Confusing a tank locomotive with a “tender locomotive” – the term means a locomotive with no separate trailing tender.
• Reading “steam” in the name as a daily guarantee – traction changes for operational reasons.
• Interpreting a repaint as a different design – colour changes nothing about wheel arrangement or running gear layout.

Conclusion

Saxon narrow-gauge steam locomotives are one of the few subjects where identification really is reliable: count the axles, check the running gear, remember the silhouette. These three steps hold true regardless of which operator is running which machine at any given time.