Obstacle Crossing - Part 2 - Suffolk Anti-invasion defences
Obstacle Crossing Demonstartion 1942- Part 2
Outcome of the demonstration and lessons learned.
Crossing first minefield.
This was done with Polish No. 2 mine detector and hand probing.
Polish No 2 Detector: Two teams consisting of one Engineer and two infantry men cleared a lane 18 ft wide by 60 yards long in approx 14 minutes. The Engineer led each party with the two infantrymen following and lifting the mines and taping the sides of the lane.
Probing parties: Two teams consisting of four men. Three men probing and one man lifting and taping the sides of the lane. They progressed at a slower rate, taking approx 17 minutes.
Crossing the Anti-tank ditch.
Hand ramping with shovels: This was carried out by Engineers (one NCO and 11 other ranks). The soil was a light sandy soil with heather and other shrub roots at ground level and after 13 minutes of intensive digging a ramp was made that was passable to a Valentine tank. During the practice sessions prior to the demonstration it was found essential to have fascines available to line the ramp out of the ditch. The fascines were made of fir tops and were six ft long by 18 inch diameter, a one man load. Work on the home side of the ramp was also advantageous to prevent the tank descending into the ditch at too steep an angle and its nose pushing the fascines out of place at the bottom of the ditch.
Explosive charges to assist hand ramping: The idea was to create a crater with sides suitable for tanks. Practices emphasized the need for carrying out trials on the same type of ground as the obstacle in order to calculate the ideal charge. Four trials were carried out during the demonstration:
1st Trial: 105 lbs of Ammonal (five 21 tins) were placed 2’ 6” down from original ground level and 2’ 6” in from the face of the ditch. This produced a crater 22 ft deep by 9 ft deep and was an obstacle to tanks in itself.
2nd Trial: 9 ft of 3” stove pipe was filled with 50 lbs of Ammonal and placed on a ledge 2’ 6” from original ground level. This produced a suitable crater but the charge failed to dislodge the heather roots, leaving an overhanging lip to the crater.
3rd Trial: A 30 lb charge of Ammonal was placed at ground level five ft back from the edge of the ditch. An ideal crater was formed but the charge was too far back from the ditch and a lip was left between the crater and ditch.
4th Trial: A 30 lb charge was fastened to a 6 ft board which was placed at ground level two ft back from the edge of the ditch. This blew the corner of the ditch off and produced an ideal slope to the ramp. However the ramp was not quite wide enough. The final design decided upon was two 15 lb charges on four ft boards placed at ground level one ft apart and two ft back from the edge of the ditch.
Right: Final design of breaching Anti-tank ditch with
Tank Fascine: These were made up of a number of 10 ft by approx 4 inch diameter forestry poles secured by a framework of scaffolding poles mounted on the front of a Valentine tank and jettisoned by the tank into the ditch, allowing the tank to cross the ditch. The fascine was assembled in a frame which was mounted on to the tank. The bottom of the outside uprights were secured to the tank by loose fitting pins fastened to towing shackles on the tank while the top of the uprights were fastened to the tank turret with 2” lashings. This required the gun to be fixed to a flank. The fascines were made of 140 poles in bundles of four wired together and placed in the frame, with single poles used for packing any gaps left by the bundles of four. When complete the whole fascine was lashed together. To drop the fascine the tank approached the ditch as close as possible with the frame lashings cut by the tank commander. The framework then pivoted on the pins, the fascine rolling out and into the ditch. The tank then drew back to draw out the loose fitting pins leaving the tank free of the frame. The tank could then drive forward and cross the ditch by riding over the fascine. The tubular framework was crushed by the weight of the tank and did not hinder its passage. It was essential for following tanks to cross the fascine centrally as there was little margin for error.
Above: Method of mounting fascine to Valentine Tank. The design was much simplified on Churchill AVRE's.
Scissor Bridge: This was carried in a folded position over the back of a turretless tank, with the bridge hinge at the rear of the tank. When the bridge was laid, the weight was brought down on three steel rollers incorporated into the launching gear in the front of the tank, on this pivot the folded bridge was swung through a 180 degrees ark. When just past the vertical the bridge began to open out. When fully opened and placed across the gap, the tank disengaged from the bridge and backed away. The bridge could span a gap of 30 ft and could be crossed by tanks up to 30 tones.
Above: Left - Scissor bridge on Valentine. Right - this shows bridge almost open on a Covenanter Tank
Second Wire Obstacle
This was cleared by standard ordnance pattern Bangalore Torpedoes 2” sectional. The minefield was approx 28 ft wide. Six five ft lengths were used giving a length of 30 ft and this cleared a 30 ft gap.
Right: Bangalore Torpedoe
This was cleared by using Snakes. These were constructed using water pipes filled with explosives. Some sections of pipe were filled with sand to add strength and prevent buckling. One NCO and five men could prepare a 400 ft Snake in five hours. The Snake was towed into position, the tank then disengaging from it and another tank following the tail of the Snake would make fast to it and push it into position detonating it electrically. In the demonstration three Snakes were used to clear gaps in the minefield. These were towed across the anti-tank ditch using a 36 ft chain and it was believed to have been the first time this was tried. The WO recommended only a 15 ft chain – this had the advantage of keeping the nose of the snake well off the ground but was not suitable for towing over a ditch. During the demonstration, although some mines 54 ft to the side of the Snake were detonated, the cleared pathway was only 30 ft in two cases and 48 ft in the third. This was less than suggested by the WO and it was thought that the Snake may have dug itself in somewhat in the sandy soil before being detonated. The recommendation from this demonstration was that tanks should keep close to the blast mark of the Snake. During the practices it was found that there was no problem in pushing a Snake over an anti-tank ditch – useful if a minefield was known to exist on the far side on an anti-tank ditch.