The Canadian Pipe Mine would appear to have been developed by Brigadier Hertzberg, Chief Engineer 7 Corps. He argued that it was by far the cheapest anti-tank obstacle at only 2s.6d per foot run. In ordinary ground it would be filled with a 2 ½ lbs charge of explosive per foot run. For roads to ensure that the road surface was broken, Brig. Hertzberg suggested 5 lbs per foot run. Trials showed gelignite was a superior charge to ammonal. Brig Hertzberg considered a charge could be bored under the road from a drainage ditch in about one hour and would provide a complete anti-tank obstacle across the road and considered it more reliable than a camoflet.
It was approved in principal by GHQ following a successful demonstration by No 1 Canadian Tunneling Company on 9 Aug 1940. The main advantage of the mine was that the obstacle was not created until needed.
The obstacle was to be typically prepared by driving 3” pipes about 55 ft long obliquely into the ground at intervals of 25 ft along the proposed alignment. The pipes were filled with explosive and prepared for firing electrically when the obstacle was required. It would produce a ditch 20 ft wide and 8 ft deep with loose earth on the sides and in the bottom, a very effective anti-tank obstacle.
Equipment needed to produce the obstacle included:
Diamond Drill Unit – a rotary drill driven by a petrol engine. Required a supply of 400 gallons of water per hour.
Pipe Pushing Machine – a hydraulic jack operated by manual power.
The drilling machine could operate over great distances through any material at approx 20 ft per hour although the pipe pushing machine could only operate in lengths of 60 ft – 80 ft in ordinary soil and would require 700 hours of operation per mile of obstacle created.
A further demonstration was held in February 1941, which also included 2nd Canadian Road Construction Company to fill in the obstacle; this Company was equipped with machinery specifically to open temporary passages through obstacles in any advance. Two methods of preparing the obstacle were demonstrated – one with the pipes pushed in from either side of the road with the pipes crissed-crossing and one with the pipes pushed in from the same side of the road, with the pipes in the same vertical plane and the lower pipe being 3 ft below the upper pipe. Both methods produced effective anti-tank ditches. The advantage of the crissed-crossed method was that it required less pushing or drilling. The second method, of pipes pushed from the same side of the road, had the advantage of being easier to connect up for firing.
Above: The two methods demonstrated, Feb 1941. The section of pipe charged is shown in red.
Commands were instructed to submit proposals for road blocks, tank obstacles etc. GHQ was to allocate personnel for carrying out the works in accordance with priorities. Each Command was allocated a reserve of pipes that would be sufficient to meet approved demands.
In Eastern Command, work began during 1941 for the employment of this obstacle. Engineers equipped and employed in Eastern Command for construction of this obstacle included 1 Canadian Special Tunneling Company, Royal Canadian Engineers and 179 Special Tunneling Company, Royal Engineers. The obstacle was to be charged when laid but not primed until “Action Stations”. Explosives used were either Blasting Gelatine, Gelignite or Nobles 808. All of these explosives were liable to deteriorate over time and required frequent inspection. The documents also state that proper consideration of removing the obstacle when no longer required needed special consideration.
As already outlined, its greatest advantage was in producing an anti-tank obstacle at the last moment. This could induce the enemy to attack at a perceived weakness or gap in an anti-tank obstacle then stopping him with a ‘surprise’ obstacle. A risk identified was that the wire from the electric firing system could be cut by shell fire.
Many pipe mines were laid/planned in Suffolk as part of defence schemes.
Above: The results of a Pipe Mine from the demonstration held in Feb 1941.
Scheme of anti-tank obstacles for the defence of Great Britain WO199/54 TNA
Eastern Command papers, TNA