The Canadian pipe mine, also known as the McNaughton tube, was a type of landmine deployed in Britain during the invasion crisis of 1940-1941. It comprised a horizontally bored pipes packed with explosives, and once in place this could be used to instantly create an anti-tank obstacle or to ruin a road or runway thereby denying its use by an enemy.
In November 1939 Lieutenant-General Andrew McNaughton travelled to Toronto for a meeting that he was anxious to attend. Those present included Lieutenant-Colonel C.S.L. Hertzberg, Commanding Royal Engineers (CRE), 1st Division, Lieutenant-Colonel Turner, Oliver Hall of the Mining Association of Ontario and Colin Campbell, an experienced mining and construction engineer who was then Minister of Public Works in the Province of Ontario and serving as a subaltern in the Royal Canadian Engineers. The meeting concerned the military possibilities raised by experimental diamond drilling, an initiative that had been broached by R.A. Bryce, president of the Ontario Mining Association, among others. McNaughton's mind had immediately seized on the possibilities such as placing explosives under fortifications or introducing poison gas into them.
As he prepared Canadian forces for departure to Britain, McNaughton dedicated a significant amount of his precious time to these possibilities and he proposed that a section of the 12th Field Company, Royal Canadian Engineers should be formed from experienced diamond drillers. He said: "We will start in a small way to see what is in the scheme and then expand if the results warrant it"[lower-alpha 2] McNaughton offered the command to Colin Campbell Campbell accepted enthusiastically and made plans to go to the mining districts of northern Ontario to get the right sort of men.
McNaughton was made General Officer Commanding (GOC) of the 1st Canadian Infantry Division. McNaughton, his staff and the bulk of his division embarked for Britain in December 1939. The Canadian forces were, however, relatively ill equipped. They were sent to spend the winter in antiquated permanent barracks in Aldershot.
Early in January 1940 McNaughton inspected the allied defences in northern France which he found to be unsatisfactory. Then on a four-day inspection of the Maginot Line he saw little to reassure him. He considered that parts of the Maginot Line would be captured should the Germans attack in sufficient numbers, but he assumed that rear defences would hold presenting the allies with the problem of retaking the fortifications. To this end, he requested – and received – working drawings of the fortifications so that his diamond drillers could help clear out German defenders.
Returning to England, McNaughton arranged a meeting with senior British engineers at Aldershot. Major-General G. H. Addision (Inspector of Royal Engineers) and Brigadier A. Sayer (president of the Royal Engineers and Signals Board) met with Hertzberg. They discussed the possibilities of diamond drilling such as cable laying and pumping poison gas into enemy defences. The British officers particularly warmed to the possibility of placing an explosive charge at the end of a long drill hole.
At that meeting McNaughton also suggested that the pipes might also be used to construct surprise obstacles in front of a German advance. This would be accomplished by pushing pipes into the ground at a shallow angle and packing them with explosives ready to be detonated. The pipe could be easily and quickly pushed by a hydraulic jack fitted to tank transporter, numbers of which were available. According to McNaughton's biographer, John Swettenham, he got the idea of using hydraulic jacks from the bootleggers of Windsor, Ontario who, during the prohibition, pushed pipes from a brewery to other premises where drink could be safely loaded.
Colin Campbell and his special section of diamond drillers arrived in England in February 1940. They started experimenting in a quarry near Aldershot and at a demonstration at Bourley Hill, Campbell proved that his section could produce surprise obstacles that could not be crossed by a tank. Although some details still needed work, attendees were impressed and promised to support McNaughton's proposal to expand the section into a tunnelling company.
In May 1940, the tunnellers were earmarked for France but the situation there was rapidly deteriorating and in McNaughton's judgement his diamond drillers could not possibly come to grips with the situation. Instead McNaughton considered that their role should be in preparing defences in England and on 17 May he advised the War Office that "the detachment of 1 Canadian Tunnelling Company, intended for experimental work in France, should not now be sent but should he held for more important experimental work in England."[lower-alpha 3]
With the fall of France, the tunnellers were, as McNaughton had planned, employed in anti-invasion measures. McNaughton noticed that ditches were being dug across unused airstrips to deny their use by the enemy even though the bombing of active airfields might make them urgently needed in the near future. By 18 June the Chief Engineer, Home Forces and the Inspector General of Fortifications were convinced of the benefits of the pushed pipes filled with explosives and set out to acquire large quantities of pipe for the purpose of destroying runways at short notice. By the end of that month the tunnellers successfully demonstrated "surprise" anti-tank obstacles near Shornmead Fort, Chatham.
The drills and pipe pushing machines were used to bury a series of 3-inch (76 mm) diameter pipes, each at a shallow angle to a maximum depth of about 8 feet (2.4 m). Each pipe was about 55 feet (17 m) long and they were placed at intervals of 25 feet (7.6 m) in an overlapping pattern such that the lower end of the first pipe would end up about 15 feet underground; the next pipe would then be pushed into the ground behind the first so that the upper end of that pipe would overlap with the lower end of the earlier pipe. The pipes were packed with explosives which when detonated would produce a very effective anti-tank obstacle about 28 feet (8.5 m) wide and 8 feet (2.4 m) deep with loose soil at the bottom. This ditch would be sufficient to either stop a tank altogether or to force it be exposed to anti-tank weapons for several minutes as it effected a crossing. Soon, such rigs were being used to drill into the approaches to bridges or embankments and left ready for instantaneous demolition.
Originally known as the Canadian Pipe Mine, it was later named the McNaughton Tube Tank Obstacle in honour of the commander of the Canadian Corps, Lieutenant-General Andrew McNaughton.
On 9 August 1940, "McNaughton's secret A/T obstacle" was demonstrated to General Brooke and met with enthusiastic approval. By October 1940, the skills of the Canadian engineers were in demand and consideration was being given to training further British units to install the devices. In due course, 179 Special Tunnelling Company of the Royal Engineers was formed. About 40,000 feet (12 km) of the obstacle were installed – requiring some 90 tonnes of explosives.
A secret report emphasised the value of this obstacle:
The quality of surprise renders the obstacle of particular value in influencing the enemy's plan. Its use enables the enemy to be induced to stage his attack at a point where there is an apparent gap in the Anti-Tank defence while at the same time retaining the ability to stop him.
It is of particular value in the last minute construction of road blocks after the passage of our troops.
It must be emphasised that surprise is the chief characteristic of this obstacle not speed.
Conventional anti-tank obstacles were very obvious from the air. These pipe mines had the advantage of being virtually invisible from the air and so could be used when the enemy had been coaxed into a seemingly weak point in the defences. Furthermore, the mines could be set in place without interference to the normal use of the land and so they were deployed under roads and railways that might need to be blocked in an instant, and runways that may need to be denied to the enemy at short notice.
However, all was not well with the McNaughton tubes. Although it had been thought that the blasting gelatine explosives would remain potent for several years, by the spring of 1941 it was evident that the explosives in some of the tubes had been affected by water and its power had deteriorated significantly. A brass spearhead on a long rod was provided for withdrawing the explosives from the tubes, but in some cases the explosive had deteriorated into a porridge-like mush. Second Lieutenant Cameron, who as a civilian was a very experienced oil drilling engineer, suggested washing out the explosives with water delivered by a narrow diameter tube pushed down the main pipe. The mush, along with globules of nitro-glycerine was caught in hessian sacks and disposed of. The original pipes were then re-charged with more stable explosives.
Soon after the end of the war, almost all the Canadian pipe mine installations were removed. However, a small number were missed and rediscovered many years later when it was necessary to deal with them with great care. This happened in April 2006 when 20 unexploded pipe mines were discovered under a runway at a former Royal Navy air base, HMS Daedalus, Lee-on-Solent, Hampshire. 60 feet (18 m) long, they were left over from an original 265, packed with a total of 2,400 pounds (1,100 kg) of explosive. Their removal, thought to be the largest of its kind in peacetime Britain, led to the evacuation of some 900 homes staggered over a 5-week period. The mines were destroyed by controlled explosion.
- British anti-invasion preparations of World War II
- British hardened field defences of World War II
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