Class 139

Updated: August 2026 – A boxy locomotive body, four axles, a freight train on the hook and a roof carrying a few more structures than usual: that’s the Class 139. It’s proof that in the German numbering system, a single technical component can sometimes decide the class designation.

What is the Class 139 (E40)?

The Class 139 is a four-axle electric locomotive for freight service, rated for 110 km/h and run on 15 kV AC. It belongs to the E 40 design, the freight variant of the German standard-design electric locomotives, and differs from the series version through an electric resistance brake.

This brake is the reason for its own class number. When braking, it converts kinetic energy into electric current, which is turned into heat in resistors on the roof. On long descending grades, that keeps the mechanical brakes cool and makes heavy trains controllable. The otherwise identical machines without this equipment run as Class 140.

E-number, renumbering, three-digit class

This class illustrates the German numbering system especially well.

• Before 1968, the Bundesbahn’s electric locomotives were called E 10, E 40, E 41 or E 50. The number denoted the design family, not the individual locomotive.
• Sub-variants got a suffix: the E 40 with an electric brake ran as E 40.11.
• With the 1968 renumbering, the Bundesbahn switched to three-digit, computer-compatible class numbers. The leading 1 has stood for electric locomotives ever since; E 10 became 110, E 40 became 140 – and the sub-variant with the electric brake received its own number, 139.
• Within the hundred-block, passenger locomotives sit in the low range from 101, freight locomotives roughly between 139 and 155, multi-system locomotives at 180 and above.

The 139 thus sits exactly on the boundary: the lowest number in the freight block. How this digit sequence relates to the twelve-digit European vehicle number is explained in the article on the UIC number and its check digit.

How to identify a 139 in the field

Where it fits in railway operations

The 139 is a line locomotive for heavy trains, not a shunter and not a passenger machine. Its use profile follows directly from its brake equipment.

Environment	Chance of a sighting	Why
Electrified steep-gradient lines	high	the electric brake is built precisely for this
Freight corridors with overhead wire	medium	fitting use profile, but a lot of competition from more modern locomotives
Marshalling yards and train formation facilities	medium	trains are made up and taken over there
Passenger routes in scheduled service	low	wrong use profile
Non-electrified lines	ruled out	electric locomotive with no on-board power source

How to systematically observe freight traffic instead of waiting on trains at random is described in the article on the freight train radar in Germany.

Spotting and photo tips

• Choose a viewpoint with a view of the roof. Because the distinguishing feature sits up top, slightly elevated, publicly accessible viewpoints such as platforms on raised ground or public bridges are especially useful.
• Prefer the three-quarter view. It shows the front, the side wall with its ventilation grilles and part of the roof section in one shot.
• Freight trains need more room in frame. Unlike a passenger locomotive, the head of the train often belongs in the shot to document the purpose of the working.
• Photograph the markings too. On machines in private-railway service, owner codes and keeper markings carry their own information value.

All shots are taken from the platform or from publicly accessible land. Tracks, operational railway land and stabling sidings are off limits; the basic rules are set out in the article on safe distance from the track.

Why steep-gradient lines need their own locomotives

The 139 exists only because a particular type of route places special demands. That’s worth understanding, because it explains why classes on the German network are subdivided so finely at all.

• Braking generates heat. A heavy freight train running downhill for many kilometres constantly converts height energy into friction heat. Block and disc brakes can get so hot in the process that their effectiveness drops.
• The electric brake works wear-free. Instead of friction, the traction motors are run as generators. The current produced is turned into heat in resistors and carried away through roof vents – the mechanical brake stays available as a reserve.
• The feature is visible. Because the resistors need cooling, they sit up top. That’s exactly how you can tell in the field that a locomotive is equipped for this use profile.
• Modern locomotives solve the same problem differently. Three-phase locomotives feed braking energy back into the overhead line and no longer need large visible resistors for it. Missing roof structures on newer classes are therefore no indication of a missing electric brake.

For spotters, that’s a useful principle: visible equipment on a vehicle almost always tells you something about the routes it was procured for. Anyone who gets into the habit of reading the roof too will recognise special equipment even on classes they’ve never seen before.

Common mix-ups

The realistically most dangerous candidates are thus the practically identical Class 140, the shorter Class 141 with a similar body shape and – from a greater distance – the passenger variants of the Class 110, which share the same basic design.

Verdict

The Class 139 is a borderline case in the best sense: technically an E 40, operationally its own class, and externally distinguishable only by the roof section and the number. Anyone wanting to identify it reliably first learns the standard-design silhouette and then consistently looks to the roof and the digits.