THE CDL TANKS OF LOWTHER CASTLE
The secret 'invasion' of Lowther Castle had its improbable origins thousands of miles away in the hot sands of Egypt. The German advance had put the safety of the suez canal in jeopardy. The problems of defending it against a night attack made the army examine methods of illuminating the canal, bearing in mind the obvious vulnerability of searchlights.
As such a device was already under consideration, it was given the code letters CDL which stood for Canal Defence Light.
The idea of attack by illumination first occured to the late commander Oscar de Thoren, RN, in 1915. His project was to use powerful projecters on motor vehicles (later tanks) to enable them to move over an illuminated field at night time. The intention was to obscure everything advancing behind the illuminated front and so completely dazzle the enemy as to render aimed fire on his part impossible. After his idea was turned down by the War office in 1917 and again in 1922, de Thoren was granted permission to submit it to the French Government. Meanwhile in England it was made public property in a thriller entitled "Eye for an Eye".
In 1933 a syndicate, known as the de Thoren syndicate, was formed, Mr Marcel Mitzakis (a British citizen of Greek parentage) was its manager. Major-General J.F.C. Fuller was its technical advisor, and the late duke of Westminister financed it. The first trial in France took place in 1934, and the second, with improved apparatus, at Chalons in 1936 which was attended by War Office representatives. It resulted in the War Office requesting the syndicate to stage a demonstration in England. This took place in february 1937 on Salisbury Plain and was satisfactory that the War Office ordered three sets of the apparatus for further trials. Exasperating delays folowed, and it was not until the night of June 7/8 1940, that the final trial took place at Lulworth. Ten days later the War Office took over the project, and put in hand immediate construction of 300 projector turrets.
The principle of the device was based on the common knowledge that if bright light falls on the eye, the pupil contracts to shut out the excess light. Conversely, if the light is suddenly extinguished the pupil dilates in an effort to increase the amount of light falling on it. The theory was that if a bright light was shone through a mechanically driven shutter, set to open and close at a certain frequency, the on looker would become virtually blind as his eyes would be continually trying to adjust themselves to ever changing conditions.
The CDL turret was divided into two compartments. The operator sat in the left hand one while the optical equipment occupied the right hand side. The 13.000.000 candlepower light came from a simply built carbon arc mounted on a cradle in the center of the light compartment, the power being supplied a 9,5 Kw generator driven by a seperate auxiliary engine in the case of the Mathilda and Churchill tanks. The intense beam of light was picked up by a reflector which was a parabola in its vertical axis and ellipse in its horizontal axis to produce a beam which converged and subsequently diverged from a nodal point some 60 to 70 inches from the source of light. This beam was reflected half way down its primary focus by an ordinary flat reflector of polished aluminium, The effect of the two reflectors was that the arc lamp could be mounted behind armour and the beam was emitted at the point where the beam converged, which was through a slot two inches in width and 24 inches in height in the front of the turret. Although this slit was vertical the light struck the target area horizontally, this was achieved by the use of the parabolic mirror. The addition of the alloy reflector prevented the mirror being shattered by the machine gun or small arms fire and, in fact, it was found that even after repeated hits, the light intensity was hardly affected.
The angle of the beam dispersion was 19 degrees which meant that if the CDL tanks were placed 30 yards apart in line abreast, the first intersection of light fell about 90 yards ahead and at 1000 yards the beam was 340 yards wide by 35 feet high. This formed triangles of darkness between and in front of the CDL's into which could be introduced normal fighting tanks, flame-throwing Churchill Crocodiles and infantry.
A further refinement was the ability to flicker the light. On the order given for 'Scatter', an armour plated shutter was electrically oscillitated back and forward at about six times a second. When first produced it was thought that this flicker effect (similar to the modern disco strobe lights) would have a damaging effect on the eyes of any observer and might cause temporary blindness. Later, blue and yellow glass screens to cover the slot were available. Their use was intended to enhance the difficulty of estimating the range of a CDL tank from an enemy position and particularly whether it was closing the range or stationary.
The first hurdle to overcome was the question of a suitable site to carry out the development trials of this top secret device with facilities for training in its use.
Lieutenant Colonel N. W. Duncan (later Major General) was dispatched to carry out an extensive reconnaissance. After looking at sites from Wales to the south of Scotland one place stood out as ideal Lowther Castle.
The disadvantage of disturbing good farming land and its close proximity to Penrith had on the other hand the
advantage of suitable terrain with ample space at the Castle for laboratories, offices and workshops. The added benefit of tire ring fence would make it relatively easy to guard, as secrecy was the prime consideration. The castle and grounds were subsequently transformed by the addition of Nissen huts on the forecourt while thousands of tons of concrete were laid between the fine avenue of trees.
During its hey-day, the Lowther coat-of-arms would be reproduced every morning in the centre of the stable yard around an ornamental fontain, using coloured chalk powders on freshly laid sand, while over thirty stable hands attended to tire polishing and grooming of horses and harness. The desecration of the 5th Earls 'holy of holies' began on the day when a Matilda tank backed up to the fountain and ripped it out of the ground.
The conditions under which the first tank was converted were primitive. Corporal F. G. Howe (later Staff-Sergeant in charge of the CDL workshops) remembers the terrible conditions with the five inches of snow on the ground. As there was no building large enough to take a tank completely, the first Matilda was converted by driving the front half into a coach-house, placing timbers over the open doors and draping them with tarpaulin sheets.
The most rigid precautions were taken to maintain security. Contracts were placed for the different components with different firms and all the equipment was sent for assembly to the CDL School. None of the stores passed through Ordnance channels and most of the CDL parts were made by Vulcans of Newton-le-Wil lows and machined at the Southern Railway workshops at Ashford.
The living conditions for the men were primitive for the first few months while Nissen huts were being built by the side of the river Lowther, near the railway viaduct. Marquees were erected, each holding three bell-tents, in an effort to give some protection from the elements. During one terrible night, a gale twice blew down all the tents. Recognising the terrible conditions the men had to put up with, the CO of the School, Colonel R. S. Ollington, gave the men five days hardship leave that first Christmas.
Having developed a working model, the next step was to demonstrate its capabilities. In complete secrecy, a CDL Matilda was transported to the Lulworth range in Dorset where Sergeant Fred Howe had volunteered to drive the tank at some risk to his life. During the day, the range had been 'swept' (all tank-tracks removed), taking on the form of a harrowed field. As darkness approached, a 25-pdr field gun was pulled out under the charge of Sergeant-Major Pat Ward, the NCO in charge of the Lulworth gunnery range, He was informed that a vehicle would drive on to his range later that night and that he must stop it using his 25-pounder with live shells.
At a given radio signal, Sergeant Howe moved off from his hidden position 2000 yards away, watched by the top brass and a nervous Colonel Ollington. With shells being fired at him at the rate of one a minute, Sergeant Howe calmly manoeuvred his tank over the range, stopping, reversing and crossing the range from side to side, all the time keeping the light dead ahead and changing the colour screens. When only 500 yards from the still-firing 25-pounder, Sergeant Howe gave the pre-arranged signal to cease fire. Sergeant Howe then pulled up in
front of the officers and each one was given a sheet of paper and asked to draw a line representing the route taken by the tank.
Almost without exception, most drew a straight line from Irish Mell Gap to their position. Then, to prove what had really happened Sergeant Howe illuminated his track marks to the incredulous officers!
The first unit to be trained at Lowther was the 11th Royal Tank Regiment, commanded by Lieutenant-Colonel H. T. de B. Lipscombe, which arrived at Lowther in June 1941. During the first week some 50 Matilda and Churchill tanks arrived. The tank crews had absolutely no idea why the security measures were so tight at Lowther. A former CDL driver, Mr. J. Part, recalled the feeling of the men when they were ordered to start removing the armament from some of the tanks, rumours soon circulating that they were being trained into a 'Suicide Battalion'.
The bulk of the training was carried out on the ranges above Knipe Scar and on the high ground running down to Emperor's Lodge. It was on these ranges that the tactical use of this device showed great promise. It was found most effective to use the CDLs in groups of four to six advancing in line abreast with beams interlocking. It was most important that at no time did the beams fall on the troops within the 'cloaks' of darkness as they would then appear in silhouette to the enemy and be easily picked off. The experienced operator was able to elevate and depress his beam ( + 10 degrees elevation to -10 degree depression) via a hand wheel at the same time checking through a dark green glass on the carbons in case of adjustment. In this way, he was able to compensate for the tank's progress over undulating ground.
It was, however, found as time went on that, when viewed from a flank, the troops in these triangles of darkness were silhouetted and it was further learned that the tanks, when not maintaining accurate station, became themselves easy targets for enfilade anti-tank fire. Various formations were evolved in order to overcome these disadvantages, f.e. the provision of flank troops equipped with CDLs to blind the enemy who were in a position to enfilade the attack.
The illuminating power of the lights was tremendous and when a squadron of sixteen tanks were operating it was possible to read a newspaper in the streets of Penrith (five miles away) on a dark night much to the wonderment of the local population who were soon trouble if a chink of light showed in the blackout. This immense volume of light presented its own problems with the constant air-raid alerts and a special telephone line, direct to the RAF early warning system, was installed to enable the light to be dowsed.
When 11 RTR left for the Middle East in March 1942, its place was taken at Lowther by the 35th tank Brigade. comprising the 49th RTR and the 152 and 155 Regiments, Royal armoured Corps. (11 RTR set up a middle East CDL school on arrival which was subsequently taken over and run by 1st tank Brigade trom July 1942 to April 1944). The 35th Tank Brigade later became part of the renowned 79th Armoured division commanded by Major-General Sir Percy C. S. Hobart.
On September 21, 1942 a letter was sent by the War Office to the local tenant farmers requesting them to attend a meeting at Penrith. At this meeting they were informed by army officers that their land would he required for military use for a period of 6 to 8 weeks. Little did they know that this would he extended to almost 2 1/2 years.
Normal life for the farmers quickly became impossible as most of the fences and stone walls were demolished and the fields churned-up by the tanks. With little or no grass left, and no hope of growing fodder crops for the winter, it soon became necessary for the farmers at Highfield, Woodhouse, Winder Hall and Celleron to sell their entire stock. Although the compensation was reasonable at the time (Highfield received £3,637.186) there was no compensation for loss of livelihood.
By the end of 1943, the authorities, sympathetic to the plight of the tenant farmers, allowed 2000 acres, now devoid of stockproof fences, to operate as an American-style ranch farm, each of the four farmers having an allocation of fifty cattle. Mr. T. Bowness of Highfield was appointed chief cowboy to ride the (tank) range on horseback. When autumn came the stock was sold leaving the farmers with a satisfactory profit.
The first large-scale demonstration took place at Lowther Castle on May 5, 1942 before Viscount Alan Brooke, CIGS, Earl Mountbatten. Chief of Combined Operations, Sir Oliver Lucas of the Ministry of Supply and a large number of the Directors from the War Office. As a result of this demonstration it was thought that the CDL, had great possibilities.
At another demonstration, American troops were placed on a hill and warned they would be attacked from a hill 1 1/2 miles away. At the start of the attack, two CDLs came round each side of the hill on 'scatter', this manoeuvre broke up the hill's outline and enabled three others to move on to the crest. When on top, they opened their shutters to display a 'steady' beam which was the signal for the two 'scatter CDLs to change to 'Steady'. The tanks moved down the hill in line abreast, in the manner already described, with troops and tanks hidden in the 'cloaks' of darkness. At the bottom lay the river Lowther with a small bridge which had to be crossed. This was achieved by the outside CDLs closing their shutters and moving across the bridge where they again opened their shutters when spaced thirty yards apart. This enabled the other CDLs and supporting vehicles to move across unseen before opening up as well. The first thing the American officers and troops knew was when the lights were extinguished revealing British troops holding fixed bajonets at their chests.
General Eisenhower was so impressed when he saw the CDL that he ordered that they were not to be used before American units had them also, and a mini-Lowther was set up at Linney Head in South Wales were US units were trained in the use of what they code--named the 'Shop tractor'. It was also laid down that this device would not be used by either British or Americans without prior approval of the British Chiefs-of-Staff. In this connection, it was considered to be inadvisable to use it in small numbers as an experiment but in large quantities as a surprise in a worth-while operation.
As more experience was gained with this device, it became clear that some of the earlier claims were exaggerated. It had already been pointed out that the scheme for using the triangles of darkness to cover the approach of assault troops necessitated using CDLs for flank protection. It was found too, that the blinding effect was not as great as originally thought. Moreover, the whole device depended on the maintenance of secrecy untill it first used as it was realised that antidotes could be rapidly improvised and the value of CDL correspondingly reduced. An even more serious setback was the discovery that the German 88mm anti-aircraft gun fitted with a green sunfilter enabled the observer to see clearly the actual slot through which the light passed.
Although the demonstrations and exercises carried out at Lowther were interesting, the highly trained operators became more and more frustrated at the lack of an operational role. At the time of the battle of Alamein sufficient CDL tanks and crews were available in the Middle East to enable this device to be used but there had been no time to train sufficient co-operating troops in that theatre. It had therefore been decided that the time was not ripe to disclose this carefully guarded secret.
In 1944, comprehensive trials with live ammunition were carried out at Linney Head in co-operation with normal tanks, infantry and artillery. The disadvantage of the Matilda and Churchill tanks had been that the main armament was lost when the CDL turret was installed. In 1943, when the American Grant became available, it was found that the CDL turret designed for the Matilda could be fitted with little modification, enabling the tank to retain its hull-mounted 75 mm gun.
Morale soared among the Lowther trained crews of the 300 Matilda, Churchill and Grant CDLs as they waited during the pre-D-Day build up. On D-Day, the British 1st Tank Brigade (which had returned from North Africa in 1943 and been reconstituted to include 11 RTR, 42 RTR and 49 RTR), and the American 10th Armoured group were fully mobilised and
