Key takeaways
- Class 399 historically carries the code Mh – the h stands for superheated steam, a marking from the Austrian narrow-gauge tradition.
- 760 mm gauge is the defining feature and the fastest route to identification.
- Don't confuse it with Class 1099: those are the electric narrow-gauge locomotives of the same line.
- The Mariazell Railway is electrified – at 6.5 kV and 25 Hz, a special case in the European network.
- Workings are appointments, not timetable services; the operating programme and vehicle availability change.
Contents
Fact file
| Vehicle type | Heavy narrow-gauge locomotive in nostalgia operation |
|---|---|
| Gauge | 760 mm (Bosnian gauge) |
| Historical type designation | Mh – the h stands for superheated steam |
| ÖBB class designation | Class 399 |
| Operating environment | Mariazell Railway and other 760 mm lines in Austria |
| Special feature of the line | Electrification at 6.5 kV / 25 Hz – a special case in the European network |
| Type of use today | Nostalgia and special-event runs, no regular service |
Identifying features
Is this really the class in front of you?
- Narrow track gauge – noticeably less than standard gauge
- A powerfully built narrow-gauge machine, larger than the usual branch-line locomotives
- Type code Mh or the class number 399 on the vehicle
- Running under an overhead line, even though the locomotive itself isn't electric
- Historic narrow-gauge coaches in the train
- Appearances practically only at announced special runs
Updated: August 2026 – Narrow tracks, tight curves, an overhead line above a train that looks like it’s from another era: Class 399, historically designated Mh, belongs to the 760 mm world of the Mariazell Railway. This page explains the type code, the line’s peculiarities, and how to reliably tell Class 399 apart from the electric narrow-gauge locomotives of the same railway.
Narrow gauge is a seasonal business
Few dates a year, changing vehicles: record every sighting with date and place in Traintrack.
What’s behind Class 399?
Class 399 is a heavy narrow-gauge locomotive for 760 mm gauge, carried in the older Austrian system as Mh. It represents the most powerful vehicle generation used on the Lower Austrian narrow-gauge lines – built for longer trains and steeper gradients than the smaller branch-line machines could handle.
Today it’s a vehicle of nostalgia operation, as maintained on Austria’s 760 mm lines all the way to the Pinzgau Local Railway. It often appears in fleet lists together with the rest of the Mariazell Railway fleet, because it runs there under the overhead line – and that regularly leads to confusion with the electric narrow-gauge locomotives of Class 1099. The difference is fundamental: the 1099 is an electric locomotive, the 399 belongs to the steam tradition of the line.
Why the code Mh explains so much
Austria worked with letters for narrow-gauge vehicles for a long time, not numbers. These codes are no accident but follow a system you can learn once and then apply everywhere.
The base letter identifies the type family. An appended h stands for superheated steam – a technique in which the steam is further heated after leaving the boiler, improving efficiency. That’s why pairs like U and Uh exist: the same basic type, once as a saturated-steam and once as a superheated-steam machine.
A second system was added with the founding of the ÖBB. Traction vehicles there are called Reihe (class) plus a number, and the number follows a clear order: two digits for standard-gauge steam locomotives, three digits for narrow-gauge steam locomotives, four digits for modern traction vehicles. For the four-digit numbers, the first digit reveals the traction type – 1 stands for electric locomotives, 2 for diesel locomotives, 4 for electric railcars, 5 for diesel railcars.
Both designations still exist side by side today. A vehicle can therefore be marked and listed as both “Mh” and “Class 399” at the same time. How the twelve-digit European vehicle number brings this information together is explained in the guide to reading the UIC number.
The line explains the vehicle
760 mm gauge
Roughly half of standard gauge. It allows tight curves and cheap construction in difficult terrain – while at the same time limiting vehicle width and axle load.
Mountain character
Big height differences and long gradients demand tractive effort. The heavier design was procured exactly for this, while smaller machines sufficed on the flat.
Electrification at 6.5 kV / 25 Hz
A special case in the European network. It's the reason the line has its own electric vehicle types that can't be used anywhere else.
Two traction types side by side
Electric vehicles run under the same overhead line, and – during special runs – steam locomotives too. That produces subjects you'll barely find a second time anywhere.
Placing it in the Austrian class scheme
| Class designation | Gauge | Traction type | Examples |
|---|---|---|---|
| Two digits | Standard gauge | Steam | Class 52, Class 77 |
| Three digits | Narrow gauge | Steam | Class 298, Class 399 |
| Four digits, starting with 1 | Either possible | Electric | Class 1099, Class 1142 |
| Four digits, starting with 2 | Either possible | Diesel | Class 2095, Class 2143 |
| Four digits, starting with 4 | Mostly standard gauge | Electric railcar | Class 4020, Class 4024 |
| Four digits, starting with 5 | Mostly standard gauge | Diesel railcar | Class 5022, Class 5047 |
For a direct comparison, it’s worth looking at the smaller narrow-gauge type Class 298 (U): the same gauge, but a noticeably lighter machine. On standard gauge, by contrast, stand classes such as the ÖBB Class 77 and the freight locomotive ÖBB Class 52 – three vehicles through which the whole class scheme can be worked through.
Two designations, one vehicle
Always note both code and class number for historic narrow-gauge locomotives – so you find your sighting again in every source.
Photographing on an electrified narrow-gauge railway
Factor in the overhead line
Above a narrow-gauge line, an overhead line looks unusually massive. Choose your viewpoint so masts and brackets don't cut through the train – or deliberately include them as a picture element, because they're part of what makes this line special.
Three further points help:
- Make use of curves. Tight radii are the hallmark of the 760 mm railways. From the outside of a curve you get the locomotive and train in one shot.
- See slowness as an advantage. Narrow-gauge trains run at a leisurely pace. You can photograph the same train at several points if the paths allow it.
- Choose cool times of day. In steam operation, air temperature decides whether the steam plume stays visible in the shot.
- Show the scale. Narrow-gauge vehicles often look bigger in photos than they are. A picture element of known size – a platform, an overhead line mast, a fence – makes the proportions legible to the viewer.
- Make use of the station stop too. During a stop at a station, markings, coupling and running gear can be photographed at leisure. Such detail shots are often worth more later than a third trackside shot of the same train.
Track areas and operational railway land are closed off
Tracks, platform edges, engine sheds, workshop areas and shunting areas are off limits – on a narrow-gauge railway just as on the main network. Vehicles move there unannounced, especially when running round and shunting before a special run. Photography is done exclusively from publicly accessible areas. What's permitted in a given case depends on local rules.
The general shooting technique is covered in the guide good photos of trains; dates for special runs can be found via the heritage railway guide. The fundamental identification order is set out in the guide to identifying classes.
Common mix-ups
It points to Class 399 if …
- the track gauge is noticeably narrower than standard gauge
- the code Mh or the number 399 is shown on the vehicle
- the machine looks more powerful than the usual branch-line locomotives
- historic narrow-gauge coaches run in the train
Look more closely if …
- several narrow-gauge vehicles are standing next to each other
- only the letter code without a class number is marked
- the locomotive is stabled cold and partly obscured
It's not a Class 399 if …
- the class number has four digits and starts with 1 – then it's an electric locomotive like Class 1099
- the vehicle is standing on standard gauge
- diesel engine noise is heard instead of steam
Verdict
Class 399 is a vehicle best understood through its line. Gauge, gradients and the Mariazell Railway’s unusual electrification explain why this type exists and why it turns out more powerful than the usual narrow-gauge machines. Two steps are enough for identification: check the gauge, read the lettering. And anyone who tells the three-digit class number apart from the four-digit one won’t confuse it with the electric sisters of the same railway either.
Quick verdict
Heavy 760 mm narrow-gauge locomotive, historically designated Mh, ÖBB Class 399 in the class scheme. Identification path: narrow gauge, type code or three-digit number. Don't confuse it with the electric Class 1099 of the same line.
Collect narrow-gauge sightings
Line, vehicle, date and photo filed together – so a few dates a year build into solid documentation.
Summary
- Class 399 stands for the heavy design of the Austrian 760 mm narrow-gauge railways and is closely linked to the Mariazell Railway.
- The old code Mh and the three-digit class number 399 designate the same vehicle.
- Anyone who knows the line understands the vehicle: tight curves, big height differences and an unusual overhead voltage.
- Vehicle availability, serviceability and event programme change constantly – always check the current status.
Frequently asked questions
What is the ÖBB Class 399?
Class 399 is a heavy narrow-gauge locomotive for 760 mm gauge, historically carried under the type code Mh. It's closely linked to the Mariazell Railway in Lower Austria and today runs in nostalgia and special-event operation. There's no longer a scheduled working in regular service.
What does the code Mh stand for?
It comes from the older Austrian designation system for narrow-gauge vehicles. The letter identifies the type family, and the added h stands for superheated steam. You find the same principle with other classes, for instance the pair U and Uh. The three-digit number 399 was added later with the ÖBB scheme.
What's special about the Mariazell Railway?
It's a 760 mm narrow-gauge railway and is electrified – at 6.5 kilovolts and 25 hertz. This combination is a special case in the European network and the reason why its own vehicle types developed there. For photographers it also means: overhead line above a narrow gauge, an unusual sight.
What's the difference between Class 399 and Class 1099?
The traction type. Class 1099 stands for the electric narrow-gauge locomotives of the Mariazell Railway – a leading 1 always marks electric locomotives in the ÖBB scheme. The three-digit 399, on the other hand, belongs to the steam tradition of the line. Both run on the same gauge and under the same overhead line.
Why do narrow-gauge locomotives have three-digit numbers?
Because the ÖBB scheme cleanly separates the vehicle groups. Standard-gauge steam locomotives got two-digit class numbers such as 52 or 77, narrow-gauge machines three-digit ones such as 298, 399 or 699. Modern traction vehicles, by contrast, carry four-digit numbers. So the number of digits alone already tells you a lot about era and gauge.
Where can I see Class 399?
At announced nostalgia and special runs on narrow-gauge lines in Austria. There's no diagram plan. Serviceability depends on overhaul deadlines, workshop capacity and staff, the programme on the season. Anyone wanting to see a particular machine checks the operator's current event announcements, not older lists.
How do I reliably recognise narrow gauge?
By the track. At 760 mm the rails sit noticeably closer together than at standard gauge's 1,435 mm, and the whole vehicle looks narrow and low as a result. Further clues are tight curves, narrow platforms and a smaller loading gauge. If standard-gauge stock is standing next to it, the difference is instantly visible.
Is it worth documenting such runs?
Very much so. On narrow-gauge lines, vehicle allocation, livery and coach sets change noticeably over the years, and operation is concentrated on a few dates a year. A dated sighting with vehicle number, place and photo is therefore often more informative than any general fleet listing online.
Log your sighting of the ÖBB Class 399 (Mh)
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
ÖBB Class 298 (U)
Class 298 – the old type U – is a narrow-gauge steam locomotive for 760 mm gauge. Here's how to identify it and find it in heritage operation.
Steam/specialÖBB Class 77
The Class 77 is an Austrian passenger tank locomotive with three coupled axles between two leading/trailing axles. Here's how to identify and classify it.
Steam/specialÖBB Class 52
The Class 52 is the Austrian version of the war locomotive: a freight steam engine with five coupled axles. Here's how to identify it reliably.
Electric locoÖBB Class 1142
The Class 1142 is the push-pull-capable development of the 1042.5 series. Here's how to recognise it and what push-pull operation means for spotters.
Electric locoÖBB Class 1010
The Class 1010 was a six-axle general-purpose electric locomotive of the ÖBB and today only runs on heritage duty. Here's how to place it and tell it apart from the Class 1110.
Electric locoÖBB Class 1012
The Class 1012 remained a small production run of modern ÖBB electrics – overtaken by the mass procurement of the Taurus. Here's how to place it and recognise it in the field.
Who is behind it
Groups, brands, manufacturers and operators – who owns whom and how to recognise them out in the field.
Bregenzerwaldbahn (Wälderbähnle)
The Bregenzerwaldbahn was a 760 mm narrow-gauge line from Bregenz to Bezau. What remains is a short stretch, on which a society runs steam and diesel trains during the summer half of the year. For spotters, it's one of the few chances to see Bosnian gauge in operation in Vorarlberg.
Heritage railwayGurkthalbahn
Carinthia once had a sizeable narrow-gauge network. Of the Gurkthalbahn, a short stretch near Treibach-Althofen has survived, on which a society runs steam trains in summer. Anyone wanting to see 760 millimetres in operation has only a few addresses left in Austria.
BrandMariazellerbahn
The Mariazellerbahn is a 760 mm narrow-gauge railway with an overhead line voltage found nowhere else in scheduled operation. The name stands for a route and a service brand – since 2010 it has no longer been run by ÖBB, but by the state of Lower Austria.
BrandPinzgauer Lokalbahn
The Pinzgauer Lokalbahn links Zell am See with Krimml – at 760 mm gauge and with diesel traction. The name describes a line; it has been run by the Salzburg AG since 2008. A flood almost cost the railway its existence along the way.
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