The collection of the Kelham Island Industrial Museum, in Sheffield, Yorkshire, UK, includes a working steam engine which is certainly the most powerful in Europe and very probably the most powerful left in the world.

The River Don Engine is unique as a result of its longevity, not because of an exceptional and original design. The company that engineered it, Davy Brothers of Sheffield, built and sold at least three others to an identical pattern within the space of a few years at the beginning of the 20th Century.

All four engines served the same purpose, providing the energy to drive a heavy plate mill. All four mills rolled the same product: steel armour plate for the hulls of battleships. This was the era of steel as the fabric of war.

The history of the River Don Engine is also the history of the industry that it served, and of an arms race to command the weapons of mass destruction of another age.

Davy

David and Dennis Davy started out as millwrights at Lady's Bridge in Sheffield in about 1830. Their dream was to make a business out of building steam engines. The first train service from Sheffield to London was pulled by a Davy locomotive, but in 1851 the brothers made a decision that inadvertently changed their destiny. They bought the Park Iron Works at Norfolk Bridge, reasoning that a steady contribution business in iron-founding would stabilise their cash-flow. Within twenty years, half of Europe's steel was being made within ten miles of their doorstep, and the tycoons of the age were soon seeking a local supplier of ever-bigger steel-processing machinery.

David was killed in a works accident in 1865, and with him went the purist's zeal to build agile locomotives. The new management took to rolling mills and forging plant, and the huge static engines needed to drive the former. This second generation of the engineering family was astute, recognising that their business advantage lay in heavy plant because of their unusually large foundry capacity. They adapted railway industry valve-gear to produce engines of immense power but also capable of exceptional acceleration. They were assiduous in securing patents, and the great steel firms were too, and a city a hundred miles from the sea made herself ready to be the dominant naval armourer of the age.

By the time of the River Don Engine, Davy Brothers Ltd had been long renowned as the engineering firm of choice to the great steel companies of Sheffield. The four-hundred strong workforce designed and built anything they were told to build. In that burgeoning city with its wild horse of a marketplace, Davy's destiny had become to fashion the biggest machines it dared.

Cammells

Charles Cammell gave his name to a famous shipyard, but he was no shipbuilder. He started out making rasps and files in a workshop in Sheffield's Savile Street. Rather like the Davys, he acquired some steelmaking with the intention of feeding his downstream business, only to find that the steelmaking had become the business.

Cammell rode the wave of demand for steel with an aplomb given to a very few, and along with a small number of others including Thomas Firth and John Brown he became rich and powerful. His prime asset was the famous Cyclops Works, but he was soon planning another.

By the end of the 1880s, the construction of warship hulls using armour plate was commonplace. The practice began some thirty years before, with forged wrought-iron cladding, before moving on to riveted rolled steel. In spite of its inland location, Sheffield remained dominant in the technology through a combination of superior hot metal capacity and technical expertise.

Since the 1850s the Royal Navy had been proceeding steadily with a programme to refurbish its fleet, but now an event took place that changed the tempo. On 25 June, 1888, far away in Berlin, Kaiser Wilhelm II succeeded to the throne of Germany. The world's first industrial arms race had begun. Charles Cammell's response was to build an entire plant to supply it. Somewhere in the rush, the tradition of high-minded classical plant-naming was forgotten and the Grimesthorpe Ordnance Works sprang up in just two years.

Grimesthorpe's first mills and engines were supplied by Davy, but by the turn of the century, the technology had moved on again. The engineers proposed a 14-foot wide mill with a 12,000 horsepower engine, around half as big again as anything previously built. At much the same time that it was ordered, Cammell's bought out Lairds of Birkenhead. Back in Sheffield, they created a mill bay so large that it acquired a nickname of 'the Cathedral'. It was 310 feet long by 64 feet wide and 50 feet high. It was served by three cranes, one of which could lift 150 tonnes, a monster for its day. The housings of the great mill were founded at Park in the Spring of 1904, and its construction inside the Cathedral began in the late summer of that year. It would be served by a 4,000-tonne slabbing press, also supplied by Davy, which was designed to break down open-hearth steel ingots from the adjacent Siemens department. The slabs would then be sent, still hot, to the single-stand mill for rolling to plate armour up to eight inches thick.

Statistics of the Engine

The River Don Engine, with her full original battery of boilers, was capable of delivering 12,000 horsepower¹. To put this figure into perspective, that's about 40% more powerful than the biggest of the plate mill stands still operated in Britain today. The total weight of the Engine is about 420 tonnes, and nearly half of that is rotating machinery. The main gear wheel alone weighs more than 50 tonnes. In spite of all that inertia, the machine is capable of reversing from a full 70 rpm in one direction, through standstill and back up to 70 rpm in the opposite direction in just two seconds.

The engineers chose a three-cylinder vertical arrangement with a 48-inch stroke and a single-piece crankshaft. Steam engine purists are sometimes disappointed to find that a single-expansion configuration is used, but there was no particular need for efficiency here. Nor was there any great need for compactness. The refinements of locomotive engineering come at the expense of maintenance complexity, and only the useful features were ever incorporated into static engines. The novel design concepts in the River Don Engine are the ones directed at securing her lightning-fast reversal. These include the Joy valve-gear and the arrangement of the outboard flywheel and reduction gearing, all packed into a tight space, with the mill drive passing back parallel to the crankshaft.

It's easy to forget that this was all engineered more than a hundred years ago, in a time when few people had yet come across the domestic light bulb. Even from our modern-day standpoint, the design is audacious and the outcome is breathtaking.

The Engine's First Home

By 1913 the Cammell Laird company was making 15,000 tonnes of armour plate a year, at two inches thick and upwards. Almost all of that production was powered by the River Don Engine. The mill and the Engine worked at Grimesthorpe for over fifty years, through two world wars and the depression between them. In 1929, as a result of that depression, Cammells combined with their former rivals at Vickers, half a mile to the south-east. The new company was named the English Steel Corporation. Nobody would have guessed it then, but the Engine was destined for a new name too.

After the Second World War, and the lessons of Pearl Harbour and Guadalcanal², the days of ever-thicker armour plate came to an end. The munitions had decisively overcome the armour. The Grand Slam bomb, itself made at Vickers' River Don Works, is another resident of the Kelham Island Museum and at ten tonnes weight is the heaviest bomb ever deployed. With destructive power like that around, and nuclear weapons now in the equation, nobody would ever again believe that a wall of steel could afford unbreachable protection.

An era of lighter plate was now coming, a decision was taken to refurbish and relocate the Engine and her mill. In 1957, the Engine turned again at the River Don Works just off Brightside Lane and about half a mile from her original home. Down in his grave, Charles Cammell might have turned too.

The Engine's Second Home

Information about the mill is much more plentiful from the 1960s onwards. There are many photographs and some film-footage, a lot of it showing birch-twigs protruding between the table-rollers. These were used to remove iron oxide (known as 'scale') from the plate surface, and it was a violent process. Shards of scale would break out with a report like a gunshot, and fly down the rolling line so far and fast that they sometimes clattered against the walls. At peak production, the mill would consume three tonnes of birch in a single shift.

By now, the mill had an electric screw-down and tables, but other features were still the basic ones of the original design. Modern plate mills have turn-tables, and can rotate the plate sideways to cross-roll it to an accurate width. The River Don mill had pneumatically-raised mushroom buttons instead. To turn the slab, the buttons literally picked up an edge and the tables slewed it round by driving against the opposite one.

The mill was a lot easier to operate in its River Don manifestation. The hand levers used at Grimesthorpe were thrown away, and remote actuation through switches saw off some of the strenuous labour. It was still a manually-intensive job, though. There were 14 men on a shift in the early 1960s, not including the furnace-men.

Right up to its decommissioning, the mill processed prestigious material and set some impressive performance figures. As well as lighter armour for the modern navy and for battlefield vehicles, it rolled plate for oil platforms and nuclear reactors. It successfully took the step to processing stainless. Even in its last weeks and under a closure order, it was called upon by British Steel to make up volume following a breakdown at the Dalzell plate mill in Scotland. One last record was broken, as the mill and its Engine produced 640 tonnes in 24 hours.

In 1974, the mill went to scrap. Though sad, there was in truth nothing remarkable about it to justify preservation. The Engine was by now a different matter. She was already the most powerful working steam engine left in Europe.

A preserved rolling mill of any great size is by simple practicality a static and sterile exhibit, but a steam engine needn't be. A few imaginative and courageous people were already committed to rescuing the River Don Engine, and not just as a museum piece. They set out to retain a fully-operable machine.

The Engine's Present Home

The places where she once stood are all faded now. The Cathedral has gone forever, replaced by a modern industrial estate. The Park Iron Works is derelict, and will never again quake to the drumbeat of huge machines. The doorway that once lead to the Engine's lair at the River Don Works is crumbling and overgrown, and the space she occupied is dark and damp, used for pattern storage for the foundry.

The process of decay was reversed at Kelham Island, however. It took four years to restore and rebuild her. The man who did more than anyone to save the Engine was the Commercial Director of the River Don Works, Hugh Wentworth-Ping. It's very poignant that he passed away in 2005, the Engine's centenary year.

Since 1983, the Engine has been in steam twice a day, four days a week. Those who've seen her are captivated, and usually a little scared, by her speed and acceleration. The River Don Engine stands as a monument to the people who made her and operated her, to their acumen and to their sacrifice.