Cultivator No.6 Winston Churchill’s Trench-Digging White Elephant

Generals, it is said, are always ready to fight the last war. Never has this adage been more true than in the years 1939-1941, when the Nazi blitzkrieg swept its way across Europe. German divisions, spearheaded by tanks and supported by ground-attack aircraft, either steamrollered over or bypassed entirely the French Maginot Line and other fortifications built to keep them out, rendering thirty years of military thought and planning obsolete overnight. Yet despite this rude awakening, many remained firmly wedded to old ways of thinking. Among these was British Prime Minister Winston Churchill, who for three years obsessively pursued the development of an enormous machine designed to dig trenches up to the enemy lines – a machine that was obsolete the moment it was conceived and ultimately proved a costly and useless white elephant. This is the curious story of Cultivator No.6.

Winston Churchill had witnessed the horrors of trench warfare first-hand. Following the failure of his Dardanelles campaign in 1915, Churchill resigned his position as First Lord of the Admiralty and joined the British Army as a Lieutenant-Colonel, serving with the 2nd Grenadier Guards in Belgium from January to May 1916. He had also established the Admiralty’s Landship Committee the year before to investigate the use of armoured tractors to break the deadlock on the Western Front. The Committee’s work eventually resulted in the development of the tank, which first saw combat during the Battle of the Somme in July 1916. Thus, when the Nazis invaded Poland in September 1939, the problem of avoiding the attritional slogging match of trench warfare was very much at the forefront of Churchill’s mind. Following Britain’s declaration of war on September 3, 390,000 men of the British Expeditionary Force were deployed to France, and many feared the German Luftwaffe would immediately commence aerial bombardment of the British Isles. However, the Germans, still hoping to broker peace with the British, did not attack, seemingly content to consolidate their gains in Poland. What followed was an eight-month period of military inactivity which became known as the “Phoney War.”

Churchill, however, was not fooled, and knew that it was only a matter of time before Hitler launched an invasion of France and the Low Countries. Though he was at the time once more First Lord of the Admiralty, Churchill cast his mind beyond purely naval matters and came up with a variety of ideas for bringing the fight to the enemy when the time came. One such idea was Operation Royal Marine, a plan to float large numbers of naval mines down German rivers to destroy bridges and other infrastructure. Another was a scheme he had first conceived during the First World War for a device capable of penetrating the Siegfried Line or Westwall, the chain of bunkers, trenches, and other fortifications protecting Germany’s border with France. As Churchill later wrote in his book The Gathering Storm:

“During these months of suspense and paralysis I gave much thought and compelled much effort to the development of an idea which I thought might be helpful to the great battle when it began… It was a method of imparting to our armies a means of advance up to and through the hostile lines without undue or prohibitive casualties. I believed that a machine could be made which would cut a groove in the earth sufficiently deep and broad through which assaulting infantry and presently assaulting tanks could advance in comparative safety across No-Man’s-Land and wire entanglements, and come to grips with the enemy in his defences on equal terms and in superior strength. It was necessary that the machine cutting this trench should advance at sufficient speed to cross the distance between the two front lines during the hours of darkness. I hoped for a speed of three or four m.p.h.; but even half-a-mile would be enough.”

The idea of tunnelling towards enemy lines was nothing new, with such attacking trenches traditionally being known as “saps” and the specialized troops tasked with digging them “sappers” – a term that was later applied to all military engineers. This process, however, had never been mechanized in the manner Churchill envisioned. Churchill first pitched his idea to the Army, but when they proved uninterested he instead turned to Sir Stanley Goodall, the Director of Naval Construction. Goodall in turn passed the project on to his assistant J.H. Hopkins, an accomplished ship designer, who assembled a top-secret team of designers known as the Department of Naval Land Equipment. Initially the project was codenamed “White Rabbit No. 6” – variously described as a reference to Alice in Wonderland or Churchill’s ability to “pull ideas out of a hat” – but was soon changed to the more mundane-sounding “Cultivator No.6” for reasons of secrecy. Churchill also often referred to the devices as the “Mechanical Mole” or simply the “Mole”. Work on the Cultivator began in October 1939 in the Grand Pump Room Hotel in Bath – the temporary home of the Naval Construction Department – under the direction of engineer Frank Spanner.

The challenge facing Spanner was formidable. While on paper the Cultivator’s task was simple – to cut a trench seven feet wide and five feet deep – aside from an experimental WWI German vehicle called the A7V Schützengrabenbagger LMG, nothing like it had ever been built before. And even then, the German device had no armour and operated almost entirely on the surface, and could thus only be used to dig trenches far behind the front lines. For three months, Spanner experimented with a variety of digging mechanisms – including a chain-and-bucket system like that used on the A7V and German open-pit coal mining machines and a large cylindrical cutter similar to modern tunnel-boring machines – until finally homing in on the most efficient configuration. His final design was driven forward on caterpillar tracks like a tank and used a large wedge-shaped plough to remove the upper two-and-a-half feet of soil and a horizontal rotating drum cutter to excavate the lower two-and-a-half feet. The profile of the trench was squared off by a number of fixed blades on the machine’s sides while the spoil was deposited on either side of the trench, increasing the height of the walls by about three feet Spanner estimated the power requirements at around 1,000 horsepower – half for digging, half for driving the machine forward.

In December 1939, Sir Stanley Goodall presented a scale model of Spanner’s design to Churchill, who immediately released £1 Million in funds towards the construction of a prototype. The work was contracted out to Lincoln-based excavating equipment manufacturer Ruston-Bucyrus Ltd, who claimed they could produce 200 of the machines by March 1941. They also proposed a larger version, nicknamed the “Officer Model,” that could dig a trench wide enough for tanks to drive through. Meanwhile, a four-foot-long working scale model was built by engineering firm Bassett-Lowke and transported by train to London. The packing case used to transport the model resembled a child’s coffin, and reportedly several onlookers respectfully bowed their heads as it was carried off the train. The model was demonstrated to Churchill on December 12, easily digging its way through a block of simulated soil made of plasticine and sawdust. Churchill was so impressed that according to one onlooker:

“…his smile of pleasure almost dislodged his cigar.”

Another demonstration followed that evening in the presence of Prime Minister Neville Chamberlain, Chancellor of the Exchequer Sir John Simon, and Chief of the Imperial General Staff Sir Edmund Ironside, who later recalled:

“At 7 p.m. I went over to see Winston Churchill at the Admiralty. He told me that he wanted to show me his “Cultivator”. I found that he had invented and reduced to a model a machine that would go through the earth at a good pace… I thought that we could make a great deal of these machines and they present the first of any possible offensive idea.”

While the French were more skeptical, Churchill eventually persuaded them to go along with the scheme, and on January 22, 1940, an official order was placed with Ruston-Bucyrus for 200 regular and 40 “Officer” model machines. As construction of the first prototype got underway, French soldiers began taking soil samples along the Siegfried Line to determine the best places for the anticipated machines to break through.

However, the project immediately ran into trouble. In order to provide the necessary 1,000 horsepower, Frank Spanner had intended to use the Royal Air Force’s new state-of-the-art Rolls-Royce Merlin V12 engine. Unfortunately, the RAF had earmarked all Merlins for use in aircraft, leaving none available for the Cultivator project. The next best alternative was the 12TP, a lightweight 12-cylinder diesel engine built by the Colchester-based firm Davey, Paxman, and Co. As this engine only put out 600 horsepower, two would be needed to drive the Cultivator, requiring extensive modifications to the design. However, the new configuration did have certain advantages. For example, one engine could now be used to dig the trench and the other to drive the machine forward, eliminating the complex gearbox previously needed to divide the power of a single engine. Diesel fuel was also significantly less flammable than the aviation-grade petrol used by the Merlin, increasing the vehicle’s survivability.

The prototype Cultivator, nicknamed “Nellie” after the initials of the Naval Land Equipment Division, was a true behemoth, measuring 77 feet long, seven feet wide, eight feet tall, and weighing 130 tons. The machine could be broken into three sections for transport, while the front excavator section could be raised and lowered hydraulically to allow the machine to ascend and descend while digging. While designed to dig in a straight line, the machine could be steered to a limited extent using hydraulically-powered flaps on its flanks. An internal conveyor belt carried spoil from the lower drum cutter to the top of the machine, where it was deposited on either side of the trench. A separate conveyor also deposited a variable amount of spoil under the machine’s tracks to keep the whole device straight and level.

In April 1940, just as Nellie was nearing completion, a new problem presented itself: another inventor had come up with a radically different method for digging trenches that was in many ways far superior to Frank Spanner’s design. The inventor in question was Cecil Vandepeer Clark, who would later become famous for inventing the magnetic limpet mine for use in naval sabotage – and for more on that, please check out our previous video That Time the British Fought the Nazis Using…Canoes. Clarke’s scheme, which he had laid out in a top-secret report for the Royal Engineers, envisioned an armoured vehicle equipped with hydraulic rams to push explosive charges into the soil ahead of it. The charges would then be detonated, blasting a crater into which the vehicle could then be driven. This scheme had the advantage of simplicity, requiring far less engine power and mechanical complexity than Nellie. It could also blast its way through minefields, bunkers, and other obstacles would have stopped Nellie dead in its tracks. However, Clarke’s machine would need to be more heavily armoured to survive the blast of its own explosions and would likely be far slower than Nellie, its estimated top speed being only 250 yards per hour. Furthermore, Nellie had been designed to advance stealthily under the cover of darkness and the noise of an artillery barrage, whereas there was nothing stealthy about a vehicle detonating a large explosive charge every few minutes. Nonetheless, when news of Clarke’s scheme reached the Admiralty, they were sufficiently impressed as to hire Clark on as Assistant Director of the NLE with a salary of £1,000. However, at this point work was too far along on the original Cultivator design, and Clark’s ideas were completely ignored, causing him to resign in frustration just two months later.

Meanwhile, the project was struck another serious blow when on May 10, 1940, the Germans launched their long-anticipated invasion of France and the Low Countries. By swinging through Belgium and the seemingly-impenetrable Ardennes Forest, German Panzer divisions completely bypassed the formidable Maginot Line and succeeded in overrunning France in only 6 weeks. This stunning defeat confirmed to many in the British Establishment that the military doctrines which had underpinned the Cultivator scheme were now entirely obsolete and that the Cultivator itself no longer had any practical use. Furthermore, with all the BEF’s tanks and equipment left behind on the beaches of Dunkirk and the nation facing the imminent threat of Nazi invasion, every available resource was needed for the upcoming defense of Britain. Yet Churchill, stubborn as ever, insisted that the Cultivator project carry on – albeit in a much reduced form. In May 1940, shortly after becoming Prime Minister, Churchill wrote to his chief military assistant, Major General Hasting Ismay, that:

“The change which has come over the war affects decisively the usefulness of “Cultivator No. 6”. It may play its part in various operations, defensive and offensive, but it can no longer be considered the only method of breaking a fortified line. I suggest that the Minister of Supply should to-day be instructed to reduce the scheme by one half. Probably in a few days it will be to one-quarter. The spare available capacity could be turned over to tanks.”

Churchill’s reasons for continuing the Cultivator project in spite of its obvious obsolescence are debated to this day, with historian John Turner ascribing his dogged persistence to his initial failure to get his “mole” idea approved during the First World War. Whatever the reason, development of the Nellie prototype – now officially designated the N.L.E Trenching Machine Mark I – carried on, the machine finally being completed in April 1941.

In May, Nellie was transported to Clumber Park, Nottinghamshire, for testing by the 769th Company, Royal Engineers. The abandoned former estate of the Duke of Newcastle, Clumber Park not only far from prying eyes but had soil conditions similar to those of Northern France. To Churchill’s delight, the machine performed exactly as designed, easily chewing its way through the soil at a speed of 3,500 feet – or around three-quarters of a mile – per hour. But the machine was far from perfect. For one thing, the conditions inside the machine were unbearable, the heat and fumes nearly causing the three-man to pass out after only a few minutes of digging. The machine also proved extremely difficult to transport, requiring the Royal Engineers to develop special heavy-duty tracked trailers to move the three disassembled sections. Meanwhile, doubts mounted as to the practical utility of the machine, with observers pointing out that the lumbering cultivator would be easy prey for German dive-bombers. As a result, the government order was further reduced from 33 to only 9 machines.

Nonetheless, the NLE team pressed on, and while construction began on four more Cultivators, Nellie was moved to Lilley Hoo in Hertfordshire for testing in heavier clay soil. It was then that the War Office issued new requirements that the machine be capable of digging a short perpendicular trench every 100 yards – something Nellie with its half-mile turning radius simply could not do. This requirement effectively killed the project, though with Churchill’s dogged support it limped on until 1943 before finally being cancelled. Stubborn to the end, Churchill insisted that five Cultivators be retained in case they were needed in combat, holding out hope that they could one day be used for their original purpose of penetrating the Siegfried Line. The machines were thus placed in storage at the Long Marston Engineer Stores Depot in Warwickshire. There they remained until 1945, when the Siegfried line was finally penetrated using conventional infantry tactics. By 1946, all five Cultivators had been dismantled and scrapped. From beginning to end, Churchill’s beloved “Mole” had been a costly and useless white elephant, squandering valuable resources at a time when Britain desperately needed them. Yet of his role in the debacle, Churchill would nonchalantly admit:

“I am responsible but impenitent.”

However, some good did come out of the project. The massive tracked trailer designed to carry the sections of the Cultivator later became the 45 Ton Tracked Recovery Vehicle, extensively used by the Royal Engineers to recover damaged tanks from the battlefield. The Paxman 12TP diesel engine developed for the Cultivator was also used to power British landing craft, with over 2,500 units being manufactured during the war. Yet more than anything, the strange saga of Cultivator No.6 serves as an important lesson for future military planners: of the dangers of clinging to outdated ideas, and the fact that dogged persistence, when divorced from good judgement, can easily lead one astray.

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