Military-Grade Awesome, Prototypes and Experiments, Pushing Boundaries

The Napier Deltic

My post (or essay) today represents a rare opportunity for me to be proud to be British, and concerns the work of D. Napier & Son Limited, who started life as a car manufacturer. After WW1 they turned their hand to concentrate on engines and became one of the most important aircraft engine manufacturers of the first half of the 20th century. Some of their most famous engines, the Sabre, Lion etc found worldwide recognition powering aircraft and racing cars, including various land-speed record holders. They might have been legendary, but they weren’t weird enough for me, which is why I want to talk about the Deltic. At the height of WW2 the Royal Navy saw merit in finding a new engine for patrol boats that was both powerful and lightweight. Before then, the petrol engine had been the mainstay of the Royal Navy patrol fleet, but were growing increasingly fed up with petrol being vulnerable to enemy fire, and catching light when they didn’t want it to. More importantly, it was felt that the Petrol engined craft (with engines from exotic marques such as Issota Frascini) were seen as being at a disadvantage compared with the German diesel-powered E-boats. Napiers’ already revered status and proven track record saw them being asked to come up with something. They already had a powerful, lightweight engine in the shape of the Culverin, which was actually a license-built version of the Junkers Jumo 204 aircraft engine. This six-cylinder vertically opposed liquid-cooled diesel engine produced 720hp, but this was deemed nowhere near enough for the Royal Navy. However, the Culverin was, with significant lateral thinking, to become the basis for the Deltic. In simplistic terms, the Deltic was basically made from three Culverins. The Culverin cylinders were arranged in three blocks in a triangular arrangement, the blocks forming sides with crankcases located at the apexes of the triangle. power is transferred to three seperate crankshafts which are geared together at one end of the engine. Known as ‘phasing gears’ these keep the power unit synchronised and provide the drive for auxilliary systems like the water and oil pumps. They also transfer the output power of all three crankshafts to a single output shaft, which is neatly threaded through the centre of the engine triangle. The whole shooting match made up a remarkably compact eighteen cylinder, valveless, opposed-piston, two-stroke diesel engine. How AtomicToasters is that?

Engine Designation D18-25B
Description Opposed Piston, Liquid Cooled, Scavenge Blown compression ignition engine
Number of Cylinders 18
Arrangement Three banks of six cylinders, forming a triangular configuration
Overall Dimensions Length 94inches, Width 69 inches, Height 90 inches
Bore 5.125inch
Stroke 7.25inch x 2
Swept Volume 5384 cubic inch total
Compression Ratio 16.2 to 1
Rated Output 1650bhp at 1500 crankshaft rev/min

With prototypes up and running, the Admiralty placed a contract with the English Electric Company, parent of Napier, in 1946 to develop and produce the Deltic engine. Development began in 1947 and the first Deltic unit was produced in 1950. Marine trials were carried out in 1952 using a captured German E-Boat with its three Mercedes-Benz engines removed, discarded and possibly ceremonially buried. Various models were built, with nine and eighteen cylinder variations being the most common. These differed by having three or six cylinders per bank respectively. Although those disgusting German units had been of approximately equal power to the new 18-cylinder Deltics the they around twice the size and a whole lot heavier. The Navy were delighted, and it went on to see service in their Dark class patrol boats and Ton class anti-mine vessels, some of which are still in service. They were also employed overseas by other Navies, including in the Norwegian Tjeld or Nasty class, which was also sold to Germany and Greece, but more suprisingly the United States Navy. The excellently named Nasty class boats served in the Vietnam War, largely for covert operations. There’s a great website about them here.

This is all well and good, and I love big, fast, menacing boats, but the Deltic to me will always be remembered by me for its other major use, powering in my mind the finest Railway Locomotive ever to grace Britain’s rusty, winding, poorly maintained, dubious safety record holding, tracks. The Class 55 Deltic.

In the 1950’s, Britains Railways were determined to haul themselves out of the steam era.. Having just defeated the hun (with notable assistance from a few mates) and wanting to ready the nation for the inexorable march towards progress, the Government hatched a modernisation plan, for which loads of new diesel engines were developed. They established themselves rapidly, and soon the Steam Era was as dead as A-line flares would be thirty years later. But the conventional engine designs that less adventurous designers were creating tended to be heavy and have a poor power to weight ratio. The Deltic engine, fresh from newfound naval success, was recognised for its 1650hp at 1500rpm, with a power unit weight of “only” 11 tons.

The Class 55 locomotive was built around two Deltic engines, its design progressing via the legendary DP1 Prototype. English Electric built the production machines in 1961 and 1962. They were employed on the high-speed, long distance express passenger services between London King’s Cross Station and Edinburgh, where their 3300 hp made light work of the journey. Twenty-two locomotives were built: they dominated express passenger services on the East Coast Main until their withdrawal in 1982 at only 20 years of age. British Rail argued that their scrapping was “because there were no services that needed their high power”. This was mainly because BR had spent the last decade developing the new Intercity 125 trains that were almost as awesome. But at that point they were also carrying out a cull of smaller locomotive classes anyway, calling them “non-standard” because few crew outside the East Coast Main Line had experience of them. Also, with several million incredibly fast, successful miles under each of them, it was simpler to get rid of the fleet than to spend money maintaining them in the specialist ways they needed. I was born in 1981, and so never had the opportunity to visit Waverley Station with Deltics throbbing away at tickover. Just the name, Deltic, is of such legend that few engineering fans worth their salt will fail to go misty-eyed on their mention. Such is their allure that six of the class are preserved and make regular appearances on special Diesel Day galas on private railways, and on railtours around the country. I may have never travelled behind one, but at least I’ve had the joy of hearing one. And now, thanks to the wonder of Youtube, you can too. [youtube][/youtube] This clip is cool because, as well as displaying something of the power of the Deltics, it also shows one of the HSTs that were ultimately to usurp them. Whenever you see footage of a class 55 you feel that the sound must have been dubbed over the top. Our instinct tells us that a diesel locomotive should make a low, chugging roar, possibly with a lot of turbo whine and fan noise on higher-speed engines. But they should never sound like these. Or, rather, they should all sound like these. That Deltic scream is an entirely unique sound, with no direct comparison I can think of in any form of mechanised transportation. That noise echoing across a gently snow tinted English landscape is one of the more memorable sounds I have stored in my internal databanks. Prior to its untimely demise, at least the Class 55s whetted the British public’s’ appetite for high-speed rail. The aforementioned Intercity 125 high speed trains (HST’s) came into service in 1981 with some overlap with Deltic services. Now re-engined, virtually all of the fleet is still giving sterling service after thirty years of service, but they will never be recognised as being as pioneering as the 55s. In a way, today’s Pendolinos, Voyagers, electrified east and west-coast mainlines, and rapid transit countrywide, were a legacy left behind by the class 55s, and the Napier Deltic engine. There’s just time to quickly mention an amusing little final development, the E.185 or Deltic Turbo Compound, related in theory to the Nomad discussed here. Starting off with a Deltic engine, and then taking the turbine stage from a Rolls-Royce Nene turbojet and inserting into the centre of the triangle, the deltic acting as the gas generator, driving the turbine with with the exhaust gases, recycling some energy that would otherwise have been lost . Napier

were hoping for 6000 shaft horsepower from this frankenturbine, eventually making 5600 before a conrod went through a head, as it had been predicted to do much above 5300hp. Needless to say, this was developed for a disappointingly brief period, Napier and the Royal Navy preferring to concentrate on pure turbines from that point, despite their higher fuel consumption. And to finish, how about a working, scale model Deltic to play with on the coffee table? Well, one Clennell Tomlinson has built just such a beast, to 1/8th scale, making it a 160cc eighteen cylinder two-stroke opposed piston engine. Of the scale in AtomicToasterness, if you ask me. The project was stated as 90% complete on the website on which I found it, here and makes me wonder how long I can live without a Zundapp or an Aerial with a 160cc Deltic installation. [Editor’s Note: This article was submitted to us by the notorious Rust-MyEnemy, aka Chris Haining, who has been a regular contributor over at Hooniverse. Make him feel welcome, and maybe he’ll contribute some more awesome articles like this one! Want to be like Rusty, and contribute to AtomicToasters? Send your article in to!]

  • FЯeeMan

    Fantastic write-up, Mr. MyEnemy, and a mind blowing engine. My whole family (well, except for my daughter, and she's a girl…) has been staring at the animation of the engine trying to wrap our brains around the whole concept. Absolutely amazing, and we're the richer for having seen it.

  • Number_Six

    Hey Rusty, on a semi-related note there are still a couple of ancient English Electric powered locomotives (Type 80?) chugging around Northern Ireland. My uncle was on one recently and it ran out of diesel, so the driver walked over to a farm and got some diesel off the farmer. They sound pretty cool but I think they're mundane old V-12s.

  • That's a slice of awesome right there. Great read, and now something else i covet.

  • Joe Dunlap

    Im just curious here. While the anamation is excellent, and
    certainly demonstrates the concept, shouldnt the lower crankshaft
    be rotating counterclockwise the the upper ones? That would allow
    them all to be geared together on a common output shaft. Other than
    that, pure awesome!

    • Nope, the only way they could make the engine work was by having one crankshaft rotate the wrong way. I love that kind of lateral thought.

  • Cheers guys, and thanks to Deartháir for hosting and correcting the myriad typos there probably was…

    • Wait, what? Typos? I wasn’t checking for those!

      In fairness, I think most of your links got lost in Word somewhere. If you feel the urge to fix it, let me know, I’ll get you proper access.

  • They took the Fairbanks Morse opposed piston engine two steps further. I happend to see a running Deltic while in the CG more then 30 years ago, I have not seen one since. Very cool!

  • Van Sarockin

    What an absurd, ridiculous, lunatic engine! It's enough to make you want to start up a machine shop and foundry. Thanks also for that informative clip from the Train Platform Channel.

  • bill

    would it be possible to make a smaller version of this, say a 6 cylinder, that could fin in say… a large sedan? 😀

  • This is absolutely incredible. I now have a deep desire to find a working example and study it.

    I also have a deep desire for a full English breakfast, and I'm not quite sure why.

  • dwegmull

    Thank you for a great article. I'm a big fan of the Deltic and I've been toying with the idea of writing about it. So thanks again for saving me the trouble 😉

  • dmilligan

    Great article Chris. I love weird old engines and the Deltic is new to me.

  • FuzzyPlushroom

    I've gone through Waverley, I've been on a few trains around Scotland, but now I truly feel that I missed out on an era. Great article, Rusty. Cheers.

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  • Ivor_St_Hill

    There is only one slight problem with the animation. It correctly shows the top right crankshaft connected to both an inlet piston and an exhaust piston. However the other two crankshafts are incorrectly shown either connected to only inlet pistons (top left crank) or exhaust pistons (bttom crank). All three crankshafts were connected to inlet pistons on one bank and exhaust pistons on the other bank of cylinders. I think the inlet and exhaust ports on the LHS bank of cylinders are shown the wrong way around. Also other sites quote the compression ratio as being in excess of 19:1.

  • pete schubel

    I'm new to the Deltic engine, never knew anything about it until surfing the net one day. The overall design fascinated me as to it's configuration, quite uniqe. After reading some posts on this and watching some videos of startups, old locomotive runs etc., I'm wondering what some of the flaws may have been as the only one obvious to my uneducated eyes would be a difficulty in servicing the internals of the lowest part. Still, at first sight, this design seemed to me to border on sheer genius, truly the work of a brilliant design team or an exceptionally gifted individual. I don't know why but this engine just intrigues me, I wish there were examples in working order close by. I'm dissapointed I'll probably never get to see one of these in action first hand. After reading the post by Mr. Haining above I agree that the Deltic did indeed suffer an 'untimely demise'!

  • V. Phillips

    Had the good fortune or otherwise to have been a test engineer for British rail in the sixties working on the Napier Deltic locomotives, A most unforgettable noise when both power units were on full static load, and now largely responsible for my poor hearing, however the sound was every bit as awesome as some modern jet fighters in my opinion. A great engine with a brilliant power to weight ratio.

  • Andy

    I've been reading about these engines for years. I'd love to get my hands on a restorable one. Are there any still around?


  • Jutdanangsax

    I used to live in a house backing onto a railway incline in London in the early 80’s and would listen to these coming through at night pulling freight. We called them ‘growlers’ for the extraordinary distinctive sound they made, quite unlike other engines. I believe there are some preserved ones still running.