Key takeaways
- Class 661 is a diesel-electric main-line locomotive of American EMD design, procured back in the days of the Yugoslav state railway.
- The nickname Kennedy dates from the time of procurement in the 1960s and has stuck to this day.
- Quickest way to identify it: no pantograph, an American-looking design, a number starting with 661.
- Diesel traction fills the gaps in the electrified network – on branch lines, in shunting and on engineering trains.
- Operational status and fleet change; for a class of this age, treat any older list with caution.
Contents
Fact file
| Vehicle type | Diesel-electric main-line locomotive |
|---|---|
| Design origin | General Motors / EMD, United States |
| Procurement | For the Yugoslav state railway JŽ; after 1991 partly taken over by Slovenske železnice |
| Drive | Diesel engine with electric transmission |
| Class number | 661 – at SŽ, the 6xx block stands for diesel traction |
| Nickname | Kennedy, handed down from the time of procurement in the 1960s |
| UIC country code for Slovenia | 79 |
Identifying features
Is this really the class in front of you?
- No pantograph, but an exhaust and a large radiator section – the classic diesel locomotive signature
- An appearance in the American tradition, with clearly different proportions from European post-war diesel locomotives
- The class number begins with 661; with Slovenian registration, the UIC country code is 79
- Used on non-electrified lines and in heavy shunting and trip working
- A powerful, deep engine sound – with this design often audible before you see it
- Liveries have changed over the decades; colour is not a reliable identification feature
Updated: August 2026 – American locomotive technology on Central European tracks: Class 661, known in Slovenia simply as “Kennedy”, is a diesel-electric main-line locomotive from the General Motors design line. It dates from the Yugoslav procurement era and is now one of the vehicles German spotters have to travel for. This page places it and shows what matters when it comes to sightings and photos.
Caught an old diesel loco? Document it straight away.
With vehicles of this generation, every recorded sighting counts – log the number, location and date in Traintrack.
What is Class 661?
SŽ Class 661 is a diesel-electric main-line locomotive of American design. Its design goes back to General Motors and its locomotive division EMD; it was procured for the Yugoslav state railway JŽ, and after Slovenia’s independence part of the fleet remained with Slovenske železnice.
The nickname Kennedy has been handed down from this procurement history and refers to the time when the machines came from the USA to Yugoslavia. It has stuck in everyday use – anyone in Slovenia who talks about Kennedy means this class and not some general type of diesel.
American technology on a European network
To German eyes, Class 661 is remarkable above all because there’s nothing comparable at home. The Deutsche Bundesbahn bought its diesel locomotives from European manufacturers; Yugoslavia, by contrast, relied heavily on American designs. The result is a family of vehicles whose layout, proportions and engine-room concept follow a different engineering tradition.
| Feature | What you can observe | Why it helps |
|---|---|---|
| Type of traction | No pantograph, exhaust, radiator section | Separates diesel from electric locomotives in seconds |
| Design line | American-style proportions | Narrows down the class family, but doesn’t replace a number |
| Class number | Begins with 6 for diesel traction | Places the vehicle in the Slovenian system |
| Place of work | Non-electrified tracks, shunting and trip working | Fits the vehicle type and confirms the classification |
| Sound | Deep, powerful engine note | Often audible before you see it, helps you get ready |
Establish the type of traction
First look at the roof. With no pantograph, any electric locomotive number is ruled out – and you're in the 6xx block of the Slovenian system.
Assess the overall impression
The American design line looks differently proportioned from European diesel locomotives of the same era. That's a clue, but not proof.
Read the class number
661 on the side of the vehicle settles it. Especially against the closely related Class 664, the number is the only reliable feature.
Record the UIC number
The full number with country code 79 makes the sighting unambiguous – important if you want to keep your collection in good order.
If you want to practise the process in general, the guide to identifying classes shows the order in which to work through features sensibly: first the broad ones, then the fine ones, and the number last.
Where diesel traction is needed in Slovenia
The largely electrified network of Slovenske železnice still needs diesel vehicles – for very practical reasons. Not every line has an overhead wire, not every track in a station is wired, and during engineering works the overhead line is regularly switched off.
This produces a pattern of use similar to Germany’s: diesel locomotives work on branch lines, in station areas without continuous electrification, on engineering and works trains, and on transfers to private sidings. Within this field, the classes share the work – Class 643 tends to cover lighter tasks, while Class 664, like the 661, belongs to the heavier main-line category. Passenger services on non-electrified lines, on the other hand, are handled by multiple units such as Class 610.
Use and fleet are subject to change
With a class of this age, condition varies considerably from machine to machine. What's still in departmental service today may be stored tomorrow. Treat every fleet figure as a snapshot and check the situation through current sightings before a targeted trip.
Know what's still running before you travel
With old diesel locos, current sightings from the community are often the only reliable source of information.
Photo tips for a diesel locomotive with character
Old diesel locomotives are rewarding subjects: plenty of texture, strong shapes, often interesting signs of wear. At the same time, they rarely stand where it’s convenient to take photos.
Prefer a three-quarter view
An angle of about 30 to 45 degrees shows the front and side at once and makes the powerful design look three-dimensional.
Look for low-angled light
In the morning and late afternoon, the light picks out rivets, fan grilles and edges. The midday sun irons exactly that away.
Listen out
Diesel locomotives announce themselves. If you listen, your camera will be ready before the vehicle appears in the frame.
Take the details too
Lettering, radiator section, cab: with old vehicles, detail shots are often more valuable than the third overall shot of the same machine.
A word on photo strategy with rare stock: the temptation to go straight for the perfect shot is strong. In practice it’s smarter to take a safe record shot first – side view, legible lettering, enough depth of field – and only then get creative. If the vehicle leaves after two minutes, at least you’ll have the proof. If it stays, you can carry on working at your leisure. This order doesn’t replace talent, but it does prevent the most common disappointment on trips abroad.
The basics – shutter speed, plane of focus, composition – are covered in the guide to taking good photos of trains. And because a trip abroad can quickly produce several hundred pictures, it’s worth reading the article on building a photo archive for spotters beforehand: if you file vehicle, date and location neatly straight away, you’ll still find everything years later.
Safety before subject
Tracks, storage sidings and depots are operational railway land and not a place to take photos from. Stay on publicly accessible areas, keep your distance from the platform edge and expect shunting movements to appear where you don't expect them.
Common mix-ups
It's likely Class 661 if …
- there's no pantograph, but there is an exhaust and a radiator section
- the design looks American-influenced
- the class number begins with 661
- the vehicle is working on non-electrified tracks or on trip working
Look more closely if …
- a similarly proportioned diesel locomotive stands alongside – the classes of the EMD family look very alike
- the lettering is weathered or partly hidden
- the vehicle is in a livery you can't place
It's not a 661 if …
- a pantograph is raised to the overhead wire
- the class number begins with 3, 193 or 541
- it's a continuous multiple unit with no separate locomotive
Conclusion
Class 661 is one of those vehicles that tell a whole procurement story: American technology, Yugoslav procurement, everyday Slovenian service. It can be identified in three steps – roof, design, number – with the number being essential to separate it from the closely related Class 664. And because older diesel generations are shrinking all over Europe, the rule here applies more than ever: document it while you still can.
In short
No pantograph, American-influenced design, number 661: that's Kennedy. It works where there's no overhead wire, can't be found in Germany – and its operational status changes faster than the lists online can keep up.
Your Slovenian diesels in one place
Number, location, date and photo recorded together – so it stays clear which machines you really had.
Summary
- Class 661 brings American locomotive technology to a Central European network – a combination that never existed in this form in Germany.
- Its nickname Kennedy recalls the procurement history of the Yugoslav era.
- Type of traction, design and class number are enough for identification; the livery doesn't help.
- Because the class belongs to an older generation, it's worth documenting it promptly with number, date and location.
Frequently asked questions
Why is Class 661 called Kennedy?
The nickname has been handed down from its procurement history: the locomotives came to Yugoslavia from American production in the 1960s, and the name of the US president of the time caught on in everyday operation. Nicknames like this are common in the railway world – they often outlast the official designations.
What is SŽ Class 661 in technical terms?
A diesel-electric main-line locomotive from the General Motors or EMD design line. The diesel engine drives a generator that feeds the traction motors – the principle that dominates heavy diesel locomotives worldwide. The class was procured for the Yugoslav state railway; after 1991 part of the fleet remained with Slovenske železnice.
How do I recognise Class 661 in the field?
First by the roof: no pantograph, but an exhaust and radiator structures. Then by the design, which looks differently proportioned from European diesel locomotives of the same era because of its American origin. The class number 661 on the side of the vehicle confirms it.
Where are Slovenian diesel locomotives used?
Wherever there's no overhead line or it can't be used: on non-electrified lines, in shunting and trip working, on engineering trains and as stand-ins. Which specific duties are currently worked by which class changes with the timetable years and vehicle availability – there's no fixed allocation.
Does Class 661 run in Germany?
No. The class was procured for Slovenian, formerly Yugoslav, operation and can't be found on the German network. That's exactly what makes it interesting for German spotters: it's a generation of vehicles you have to travel for – American technology on a European network.
How do I tell the 661 apart from Class 664?
Both come from the same American design tradition and therefore look more alike overall than is usual with European classes. So the only reliable feature is the class number on the side of the vehicle. With these two classes, don't rely on your first visual impression.
Is Class 661 still in regular service?
The status of individual machines of such an old class varies widely, and a blanket statement wouldn't be credible. Some vehicles of this generation are in departmental service, others stored or in heritage care. Check the current situation using sightings from the recent past, not older fleet lists.
What should I look out for when taking photos?
A clean three-quarter view with a legible vehicle number, and low-angled light that brings out the structure of the design. And your location: track areas and operational railway land are off limits. Photograph from platforms, public paths or bridges, and keep your distance from the platform edge.
Log your sighting of the SZ 661
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
SZ 664
Class 664 is Slovenia's diesel-electric mainline locomotive of American origin. Here's how to tell it apart from electric locomotives, multiple units and the related 6xx classes.
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