Class 18.4–5 (Bavarian S 3/6)

Updated: August 2026 – Before there were standard-design locomotives, every German state built its own – and Bavaria’s contribution, the S 3/6, was one of the most elegant express locomotives ever to run in Germany. At the Deutsche Reichsbahn it became Class 18.4–5. This page explains both naming systems, the recognition features, and how to get a sighting.

What is the Class 18.4–5?

The Class 18.4–5 is the Reichsbahn’s designation for the Bavarian S 3/6, an express steam locomotive with a tender and 2’C1’ wheel arrangement. It was built by Maffei in Munich, across several series between 1908 and 1931, with a four-cylinder compound engine and a top speed of 120 km/h.

The build period is remarkable. Over more than two decades the same basic design stayed current – first as the flagship of the Bavarian state railway, later as part of the Reichsbahn’s fleet. That makes the S 3/6 one of the longest-lived German express-locomotive designs of all. Today the surviving machines are museum vehicles; there’s no regular service left.

Two naming systems, one vehicle

Anyone who works with German steam locomotives inevitably comes across two parallel systems: the class designations of the state railways, and the Reichsbahn’s numbering scheme from 1925 onward.

Both systems still run side by side today, because museum vehicles are often restored to the condition of a particular era. The same locomotive can therefore be marked as an S 3/6 or as an 18 4xx. The guide to identifying rolling stock classes shows how to approach such double designations systematically.

State railway or standard design? The differences

For field identification, the most important step is placing the locomotive in the right era. Pre-unification and standard-design locomotives look fundamentally different once you know what to look for.

Feature	Pre-unification locomotive like the S 3/6	Standard design like the Class 01
Era of origin	before 1920, some built through into the 1930s	from 1925
Design language	delicate, many individual fittings	smooth, functional, standardised
Chimney	tall and slender	short and stocky
Number of cylinders	often four, some in compound arrangement	two or three, usually simple expansion
Designation	class like S 3/6, P 8, G 10	class number like 01, 03, 44

From the parallel Prussian world comes the widespread Prussian P 8, which was placed in Class 38 – the same principle, a different letter, a different job. The counterpart on the standard-design side is the Class 01. And that the class number 18 later had to serve special cases too is shown by the record-breaking 18 201, which has technically nothing to do with the Bavarian design.

Where you’ll find an S 3/6

Exclusively in a museum setting. Surviving locomotives of this class stand in museums such as Lokwelt Freilassing or belong to collections; they’re only moved on special occasions and with considerable effort. For your research, that means: the route runs through institutions, not timetables.

• Museums and collections are the first port of call. There you can find out whether a vehicle is on display, in storage, or operational.
• Heritage railway event calendars list running days, anniversaries and vehicle meets where historic locomotives are shown.
• Community forums report short-notice changes and transfers first.
• Special exhibitions are often the only chance to see rare vehicles away from their home base.

The heritage railway guide describes where these sources converge and how to work through them efficiently.

Photo tips for pre-unification locomotives

Old machines with plenty of visible running gear call for different shot ideas than smooth standard-design locomotives.

• Shoot from the side, not head-on. The four-cylinder running gear is the special feature of this design and only visible from the side.
• Details are worth it. Chimney, boiler fittings, works plate and markings tell you more about the era than any overall view.
• Watch the light in the museum. Hall lighting is usually mixed and dim; a tripod ban is common, so high ISO values are the rule.
• Document the condition. Museum locomotives get repainted and relettered – how a machine looked on a given date is a genuine piece of information.

The technical basics specifically for steam are covered in the guide to steam train photography.

The state railways’ class systems at a glance

Before 1920 there was no single German state railway, but several state railways each with their own naming systems. Anyone wanting to place historic vehicles inevitably runs into these systems – and they’re more logically built than their reputation suggests.

Bavaria used the letter for the purpose and a fraction for the axles: S 3/6 means an express locomotive with three of six axles powered, P 3/5 correspondingly a passenger locomotive with three of five. Prussia went about it differently, combining the purpose letter with a running design number: P 8, G 10, T 12. Here too the letter gives the purpose – P for passenger train, G for freight train, T for tank locomotive – but the number says nothing about the axles, only which design it is.

Both systems were folded into the Reichsbahn’s class scheme from 1925 onward. The basic logic survived: purpose determines the number range. Bavarian and Prussian express locomotives became classes between 01 and 19, passenger locomotives classes between 20 and 39. Museum vehicles today carry one designation or the other depending on the era they represent – sometimes even both at once, on different parts of the vehicle.

Common mix-ups

Verdict

The Bavarian S 3/6 is the best entry point into the world of state-railway designations: its name explains itself once you know the system, and its Reichsbahn number shows how, in 1925, many separate systems became one. Technically, its four-cylinder compound engine represents an era that ended with the standard-design locomotives. Today you only meet it in a museum – but there, in a condition few other vehicles of its time can match.