Walk into any heritage railway gala in the UK today and you'll likely hear a sound that feels entirely out of place for a diesel. It isn't the rhythmic thumping of an English Electric or the high-pitched scream of a Deltic. It is something smoother, more sophisticated, and—honestly—a bit more "German." That’s the British Rail Class 35, better known to anyone who loves a bit of grease and history as the "Hymek."
These things were weird. In a 1960s Britain that was desperately trying to figure out how to stop using steam, the Western Region decided to go its own way. While everyone else was building diesel-electric locomotives (basically a giant diesel generator on wheels), the "Western" went for diesel-hydraulics. The Hymek was the mid-sized powerhouse of that experiment.
You’ve probably seen them in old photos—dark green with that distinctive lime-green stripe along the bottom. They looked fast even when they were sitting still. But beneath that stylish exterior, designed by the folks at Wilkes and Ashmore, was a mechanical heart that eventually led to their premature death.
The German Heart of a British Icon
Basically, the British Rail Class 35 was a bit of a mongrel. It was built by Beyer, Peacock & Company in Manchester, but the technology inside was pure West German. We're talking about a Maybach MD870 V16 engine paired with a Stone-Maybach-Mekydro hydraulic transmission.
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That’s where the name comes from: Hydraulic Mekydro. Hymek.
The idea was simple. Hydraulic transmissions are lighter than heavy electrical generators and motors. If you can make the loco lighter, you can accelerate faster and save on fuel. It worked, too. For a "Type 3" locomotive (around 1,700 hp), the Hymeks punched way above their weight. They were often seen hauling 14-coach passenger trains out of Paddington, a job usually reserved for much bigger engines.
Where They Actually Ran
If you lived in Bristol, Cardiff, or anywhere along the line to Worcester back in the day, the Hymek was your daily bread. They were everywhere.
- Old Oak Common (London): Handling the semi-fasts to Oxford and Hereford.
- Bristol Bath Road: The heart of the fleet, working everything from secondary passenger turns to heavy freight.
- Cardiff Canton: Keeping the South Wales main line moving.
I’ve heard stories from old drivers who said the Hymek was the best thing they ever drove. It was responsive. It didn't "hunt" for gears as much as the bigger Westerns did, at least until you tried to use them for "banking" (pushing trains up hills).
There’s a famous bit of railway lore about the Lickey Incline near Birmingham. The Hymeks were sent there to help push heavy freight trains up the 1-in-37 grade. The problem? The speed of the train usually hit exactly the point where the transmission wanted to shift between first and second gear. The poor locos would just sit there "hunting"—shifting up and down constantly—until the crews probably wanted to pull their hair out.
The Short, Brutal Life of the Class 35
British Rail built 101 of these locomotives between 1961 and 1964. By 1975, they were all gone.
That is a ridiculously short lifespan for a locomotive. Some were scrapped before they were even ten years old. Why? It wasn't because they were bad engines. In fact, many enthusiasts and engineers argue they were the most successful of all the diesel-hydraulic designs.
The real killer was standardisation.
In the late 60s, British Rail decided that having a "non-standard" fleet in one corner of the country was a logistical nightmare. They wanted diesel-electrics (like the Class 37) everywhere. The "National Traction Plan" basically signed the Hymek's death warrant.
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It's sorta tragic. You had a fleet of reliable, powerful, and popular locomotives being cut into pieces for scrap just because they didn't fit a corporate spreadsheet.
What’s Left Today?
We got lucky. While most of the fleet met the torch at places like Swindon or Cashmores in Newport, four survived.
- D7017: The first one saved, now a legend on the West Somerset Railway.
- D7018: Also at the West Somerset Railway. It’s had a long road back to health but is a beast when it's running.
- D7076: Based at the East Lancashire Railway.
- D7029: Owned by the Diesel Traction Group and often seen on the Severn Valley Railway.
Seeing one of these in the wild today is a trip. When D7017 or D7018 starts up, there’s this momentary silence, then a sharp clatter-clatter-clatter as the Maybach engine finds its rhythm. It doesn't sound like a modern train. It sounds like a piece of high-performance machinery from a different world.
Why You Should Care About the Hymek
The British Rail Class 35 represents a "what if" moment in history. What if BR had stuck with hydraulics? They were lighter, arguably more efficient, and definitely more stylish than the boxy diesel-electrics that replaced them.
Honestly, the Hymek is the underdog that proved its worth but got sidelined anyway. It's the classic British story of engineering brilliance being undone by shifting policies.
Actionable Insights for Fans and Travelers
If you want to experience a Hymek for yourself, don't just look at photos. Here is what you should actually do:
- Visit the West Somerset Railway: This is the spiritual home of the preserved Hymeks. Check their "Diesel Gala" dates; that’s when you’re most likely to see D7017 and D7018 running in tandem.
- Listen for the "Maybach Bark": When the loco is under load, the exhaust note changes significantly. It’s a treat for the ears that you won't get from a standard Class 66.
- Look for the Cabside Numbers: Unlike most BR diesels of the era, the Hymeks had cast aluminium numbers on the side. It’s a small detail, but it shows the level of "custom" design that went into these machines.
- Check the Timetables: Heritage lines like the East Lancashire Railway often run "Diesel Saturdays." Call ahead to see if the Hymek is the rostered loco for the day.
The era of the hydraulic might be over on the main lines, but on the preserved tracks of the UK, the Hymek is still very much alive, kicking, and screaming its way through the countryside. It’s a loud, vibrating, green reminder that sometimes, the "non-standard" way was actually the better way.
To get the most out of your next visit to a heritage line, check the Diesel and Electric Preservation Group (DEPG) website for the latest maintenance status on D7017 and D7018. They provide real-time updates on which locomotives are fit for traffic, ensuring you don't miss the chance to hear that Maybach engine in person.