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off in lengths of 1 or 2 feet they made excellent road mines.
The pipe, filled with H.E., and stopped at each end by a well-waxed wooden plug, would be buried just under the surface across the wheel-track on one side of the road. A small wooden chock under each end of the pipe would hold it in position, and under the chock at one end a pressure switch would be placed, from which instantaneous fuse led through a hole in the wooden cork to the primer inside the pipe. The pipe acted as a lever and, when the wheel of a vehicle went over, put pressure on the switch and set the mine off. Apart from wrecking the wheel, the splinters from such a mine had sufficient velocity to penetrate the under part of a truck and kill the people inside.
After a time, when we heard the Japanese had discovered what type of mine we were using and had successfully taken one or two up, we taught our students to add a release switch under the chock at the other end, with fuse leading into the pipe through the other cork, so that when the Japanese located such a mine and started to take it up, it would go off in their faces.
Very early on, we were confronted with the problem of protecting the civilian population. One of the first mines put down on a road in the Triangle blew up three country women. For a long time, the solution of the problem eluded us. It only required 35 lbs pressure to set the mine off, until we discovered we could increase this to 200 lbs by cutting a small metal collar out of a cigarette tin and fitting it round the neck of the plunger on the switch. At 200 lbs, the mine could be trodden on with impunity, but a lorry would set it off. We had trouble too with our instantaneous fuse, which we found hesitated in action, so that sometimes the lorry would be ten yards past the mine before it exploded. In the end, we abandoned instantaneous fuse and substituted detonating fuse, which meant fixing your detonator direct to the switch instead of placing it inside the primer in the pipe.
Another serious problem was that of waterproofing. Mines and booby-traps must be protected from damp because, although some explosives, such as 808, are not affected by water, if any damp gets into the detonator, the primer, or at either end of the fuse, or in the cap of a switch, the mine will fail. The usual practice is to draw a rubber sheath over the primer and detonator assembly, and if the charge is for use under water, sometimes the whole of it is placed in a waterproof rubber bag. Unfor-