In 1939, Winston Churchill feared that the French Maginot and the German Siegfried lines would develop into wasteful stalemate trench warfare as in WWI. He conceived and pursued the construction of a trench digging machine which would allow the Allies to assault the Siegfried line. His vision was that a fleet of these machines would be assembled along the front line. During the night under a large artillery barrage to cover the noise, the machines would advance across the short distance to the German west wall reaching it by daybreak. The infantry and vehicles following in the trenches cut by machines would then be below the range of the German guns and be able to attack the enemy by surprise and secure a breakthrough. Originally the code name of the project was “White Rabbit Number Six” which was supposedly due to Churchill’s fondness for unusual hats and his ability to pull ideas out of his hat. Later on the project code name was changed to “Cultivator No. 6”.
Churchill, being the First Lord of the Admiralty, called upon the resources of the Naval design departments. Design work started just after the war broke out in September 1939. Churchill’s ‘mole’ became a theoretical possibility by the Department of Naval Constructors and the practical experience and manufacturing facilities of the commercial earth moving equipment manufacturer Ruston-Bucyrus, Limited located in the city of Lincoln. A small working model (one inch scale 1:12) of the proposed design was manufactured by the model making firm Bassett-Lowke Limited of Northampton was ready by January 1940. After a demonstration to Churchill and other authorities proving that the principles of the design was sound, permission was given to press ahead with building the machine. The official order was placed with Ruston-Bucyrus, Limited on 22 January 1940 and the Admiralty received Treasury approval for the production of 200 narrow type ‘Infantry’ trench diggers and for 40 of the wider ‘Officer’ version intended for tanks on February 7. Completing the design work and the manufacture of the machine began in earnest.
On 14 February 1940, a special top secret organization to be known as the Department of Naval Land Equipment (N.L.E.) was setup under the control of the Ministry of Supply. The new department was put in charge of the project and the code name was changed to “N.L.E. Tractors”. Arrangements were made for a production rate of twenty trench diggers per week provided that the project received top priority in all matters.
The pilot machine was officially known as the “N.L.E. Trenching Machine Mark I” but was nicknamed “Nellie” which was derived from the initials N.L.E.
The original design was based on the use of 1000 H.P. Rolls-Royce Merlin engines which would provide the high power needed for the trench digger machine but the Air Ministry declared that the all available Merlin engines were required for the RAF because all their fighters along with the Lancaster, Halifax and Mosquito bombers were powered by the Merlin. The design was then reworked to use two Paxman-Recardo 600 H.P. diesel engines (already in use by the Royal Navy) which increased the size and weight of the trench digger resulting in its traveling speed reduced from one mile per hour to one kilometer per hour. One engine drove the cutting mechanism in the plough section while the second one propelled the machine. The noise produced by the two engines would been deafening inside the machine so to counteract this special silencers were designed and installed. There were five tanks in the fuel supply system with a total capacity of 575 gallons (2176.6 Liters) which was enough fuel for approximately ten hours of digging and using full power of both engines.
The machine was 77′ 6″ long, 8′ 5″ wide, 10′ high and weighed 130 tons. The wire rope rigging fitted along the top of both sections of the machine was to defect barbed-wire entanglements over the conning tower, track pads and other protrusions.
The main body of the machine was similar to the WWI American prototype Steam Tank (above) and the British the Mark IX tank (below) which was designed to carry troops and supplies making it technically the world’s first armoured personnel carrier (APC). Production of the Mark IX tank came too late to be used in combat in WWI but they were used for some years after the war during training.
The machine was able to dig a trench 5′ deep and 7′ 6″ wide. Its digging speed was between 0.42 and 0.67 miles per hour and its traveling speeds on the surface were 3.04 miles per hour moving forward and 1.62 miles per hour in reverse. It was only designed to dig through light to heavy soils which limited the type of terrain where it could operate. The weak link of the machine was the cutting cylinders where a quite small tree trunk could jam or damage the cylinders. Since the most of machine was below ground in its own trench and obscured by the two spoil banks along side of the trench, no heavy armour plate was used on the machine making it vulnerable to artillery fire and air attack.
On 10 May 1940, the German Blitzkrieg bypassed the French Maginot line where the Panzer Divisions drove around the northern end of the line through Belgium and this maneuver removed the main purpose for Churchill’s ‘mole’. Despite the situation in France, Churchill and other interested parties continued to press forward with the project with the belief that they might still be of service in some special role or for cutting emergency anti-tank trenches in the event of a German invasion of Britain. The proposed production rate for the trench diggers was cut back to one half and with the added provision that the rate might be further be cut to one quarter resulting in no more than 60 machines could be built.
To check the design and power requirements of the two cutting cylinders that would be mounted on the front of the machine, a test rig with one cylinder was designed and built at the Lincoln works. The test rig under underwent test trials in a field at Skellingthorpe southwest of Lincoln. On the morning of Sunday, 19 May 1940, Churchill arrived at Skellingthorpe unannounced to check on the progress of the trails of the test rig. Churchill witnessed a special demonstration of the test rig in action and was pleased with the progress. Despite the worsening conditions in France, Churchill urged that work to be continued on the narrow ‘Infantry’ pilot machine even when there was no definite use for the trench digger. After the trails were completed, the test rig was returned to the Lincoln works where it was dismantled and all but the reusable parts were reduced to scrap.
The test area was located just west of the large house still known as Stones Place and was accessed by a road immediately west of the house (Birchwood Ave today). Soon after the trials, the area was absorbed into the wartime Skellingthorpe airfield. Today, the area was obliterated by modern housing developments. The red dot is location of Stone house and the circle was the approximate location of the test area.
Work continued where four test machines were built and in early 1941 the construction of the pilot machine began. Many problems had to be overcome during the manufacture and erection stages of the test and pilot machines at Lincoln. Since the project had been given to the Admiralty, the same high standards of workmanship was expected as though it was a ship that was being built, not a trench digging machine which would had a short life expectancy. On one inspection visit, the naval inspectors had one of the rivets on the machine be removed so they could check that the drilling for the head was correct. They found that the angle of the countersink was incorrect and they insisted that all the rivets be removed and the holes be re-countersunk to the correct angle specified in the plans. Another of the requirements laid down by the naval inspectors was that the machine’s fuel tanks must be cleaned out using a particular acid. However, supplies of the acid was not obtainable in time so a labourer had to climb into each tank and spent a considerable amount of time cleaning and descaling the inside surfaces before the tanks were pressure tested. These and many other interruptions caused delays in the project.
The track section of the machine was at that time the longest tracked vehicle that was ever constructed. To transport the trench digger required the machine to be split into three heavy sections (Plough Section – 30 tons, Propel Section front – 45 tons, and Propel Section Rear – 55 tons) where each section were transported by a special designed trailer. Special portable towers equipped with hydraulic jacks raised each section to a sufficient height to allow the special trailers to be moved underneath. The superstructure of the trailer was mounted on two axles each fitted with two crawler units. The type D25 tracks were designed to carry heavy loads over soft ground. One of these N.L.E. trailers was later demonstrated before the War Office at Wokingham on 12 October 1943.
Construction of the pilot machine was completed at the beginning of May 1941 and the shop trials began on May 4th. The shop trials consisted of starting the two engines and driving only the track portion out of the bay in which it was assembled across the road and then it was driven back into the bay again while at the same time tested various functions. After passing the shop trials without mishap, the pilot machine was ready to test its capabilities in field trials.
The pilot machine underwent its trails in Clumber Park, Nottinghamshire. The test area was to the south of Clumber lake in the area generally known as the South lawn.
It took a lot of time and effort to transport the individual sections of the pilot machine and all its supporting equipment and personnel to the park. Reassembling the pilot machine was completed at the end of June 1941 and it was ready for the series of field trials which lasted over six months and into the severe winter of 1941/42. The trails were under the control of the British Army and a company of Royal Engineers that were encamped in the park. The following photos were taken on 25 July 1941.
The plough section of the machine showing the plough blade with its mould boards and the twin cutting cylinders beneath.
Rear three quarter view of the machine. The white line painted along the side indicated the normal ground level during digging operation.
The crew of three entered the machine through the conning tower climbing down an iron ladder. Once at the bottom of the ladder, the driver slid to the right side and into his seat. The engineer slid to the left side and went aft down a narrow passage that ran along side the engines and then through a submarine type bulkhead hatch to his position in the rear. The pilot or navigator was the last crewmen to enter the machine and sat on a seat within the conning tower.
The engine compartment hatches of the pilot machine are open with technicians readying the engines. In the engine bay on the right can be seen the bulkhead hatch to the rear gear-box compartment and the engineer’s station. The engineer’s function was to monitor the engines, fluid couplings and other machinery in the machine. A hinged cover in the roof was provided as an escape hatch for the engineer.
The driver position of the machine with the driver facing to the rear. Instrument panels and electrical control panels were fitted to the bulkhead and included was an instrument for measuring the distance traveled by the machine. This consisted of a piano wire fed from a storage drum to a counter driving pulley with a circumference of 12 inches and the wire passed through the left side of the machine. At the start of the run, the end of the wire was securely anchored into the ground. The gear ratio between the driving pulley and the distance indicator dial was 3 to 1 which recorded the distance traveled in yards. All operations were directed by the pilot from the conning tower where a speaking tube was fitted between it to the driver’s station. Except during servicing, the side door would be permanently closed and secured with 54 bolts. The driver position was below ground level while the trench was being cut.
The left side of the pilot machine. A large “V’ for victory was crudely painted on the side.
The pilot machine at the start of a run. The twin cutting cylinders beneath the plough blade are beginning to cut into the top soil as the plough section lowers. The spoil is flung away from the machine by the lateral conveyors. Note the amount of dust and exhaust fumes.
A view of trench with the spoil heaps along the trench. A hinged door on the side of the machine enabled it to change direction by opening and pushed against the side of the trench by means of a hydraulic cylinder. The machine had a turning radius of
between 2 to 3 miles.
The pilot machine crossing an anti-tank ditch moving from left to right. Note the large “V” on the right hull side.
The machine had re-entered the trench. This photo shows the function of the plough blade which removes the top half of the trench and pushes the removed spoil away from the edges of the trench. An additional rode of the plough was to unearth any land mines that were in the path of the machine. On September 12, the pilot machine successfully advanced through a mine field and unearthed 16 mines without exploding them. During the period when testing the mines, the personnel found it more prudent to walk in the trench when crossing the site rather than the risk of climbing over the spoil heaps which may contain unexploded mines.
On 15 August 1941, a demonstration was given before the Army General Staff and as a direct result of this demonstration the War Office instructed the Ministry of Supply to suspend all further production until a wide ‘Officer’ prototype had been constructed. However in late August, Churchill countermanded this command and placed an order for four production narrow ‘Infantry’ versions and twelve of the wider ‘officer’ version.
Up to this point in time, Churchill had never seen his built ‘mole’ in action, so arrangements were made for an official demonstration for Churchill on 6 November 1941. Here Churchill views his completed ‘mole’ prior to the demonstration run.
Another photo: IWM MH 956
This is the trench made by the pilot machine on November 6 which shows some problems which the infantry would had encountered following behind the machine in actual combat. Note the collapsed sections of the trench side walls and the uneven trench floor made by the tracks. If it was raining the trench would probably be filled with water or become very muddy.
After the field trials at Clumber Park ended, the pilot machine was finally handed over to the British Army. On 19 February 1942, the 796 ME Company officially took charge of the pilot machine along with all its spares and by the 25th had accepted full responsibility for the complete operation and servicing of the machines. The ground at Clumber Park was considered too soft so the field trails of the pilotmachine was continued at a more difficult site at Lilley Hoo, southwest of Hitchin. The machine was specifically designed for the loams found in the French and German border region and the continued trails at Lilley Hoo proved to be too much for the pilot machine.
The plans existed for the wider ‘officer’ machine that would been able to dig a wider trench so that tanks could follow behind the machine. The machine would have a ramp on the rear which upon reaching the objective enabled the following tanks to climb over the trenching machine and immediately go into action but the ‘officer’ machine was never built.
With the completion of the field trials of the pilot machine and the dwindling priority of the product, the N.L.E. offices at Lincoln were closed down at the end of 1941 and the N.L.E. personnel were transferred to other locations. It is stated that the Lincoln facilities of Ruston-Bucyrus, Limited had switched to the production of tanks for the rest of the war.
In December of 1942, the Ministry of Supply relinquished control of the N.L.E. department and its projects and personnel was absorbed by the department of Armoured Fighting Vehciles. From that point forward, trench digger project began to sink into obscurity. The Ministry of Supply continued to press for the closure of the project. On 1 May 1943, Churchill finally agreed and cancelled the project although he added a rider that the machines that were already completed should be kept in good order – “Their turn may come”. On 13 March 1944, the four test machines and the pilot machine were moved to the Royal Engineer stores at the Long Marston Engineer Stores Depot (1ESD) in Warwickshire.
The project was not a complete waste of time and resources. The Paxman-Recardo diesel engines used for the machines were later modified for marine use and mass production of the engine powered all the WW2 British-built tank landing craft (3 engines in each) which played a major role in the Normandy landings.
After additional development, the special trailer was eventually used as a recovery trailer named the 45 Ton Tracked Recovery Trailer which was designed by Cranes (Dereham) Limited and was manufactured by Boulton Paul. The trailer had four Orolo track units that were unpowered with no brakes and the flat platform had chocks and ramps. A winch in an armoured compartment was mounted on the front.
This is my close up of IWM B 8035
The 45 Ton Tracked Recovery Trailer was employed by the British 79th Armoured Division. A diesel railway locomotive is being carried ashore from a LCT on Juno Beach at Courselles, 26 July 1944.
The Army kept the machines in storage and once the need for keeping them had completely passed the four test machines were scrapped ironically with the help of German prisoners of war. The last machine which supposedly was the pilot machine was kept on the specific instructions of Churchill that one example must be kept. However, once Churchill was out of position of authority, his directive was dismissed and the last machine was finally scrapped at some time in the mid 1950’s. The depot in Warwickshire was sold to St Modwen in 2004 and is now a housing development called Meon Vale.
In his memoirs after the war, Winston Churchill stated about the project:
“I am responsible but impenitent”
Giesbers Models Kit 042 N.L.E. Trenching Machine Mark I (Nellie) 1/76 Resin kit
Vendor: Black Lion Decals Online Shop
Vendor: Tracks & Troops Online Shop
Shapeways 3D Printing: 1/300 Nellie Cultivator No.6