116. Electric Railway Mine

a. Description.

(1)

Mine. The electric railway mine (fig. 145) consists of a wooden case, 9 inches square and 4 1/4 inches high, containing a main charge of 8.5 pounds of explosive. The lid is secured with screws. A rubber ring is fastened to the fuze well in the lid. The brass pressure cap of an electric railway mine fuze (fig. 146) protrudes through the rubber ring and an antilifting plunger protrudes about 1 inch above the brass pressure cap. An access hole at one corner of the lid receives the electric detona-tor, which is connected to the separate antilifting circuit. The energy is supplied by a 4 1/2-volt battery which is housed in a small wooden box inside the mine. The clockwork delay mechanism, with the main detonator, is inserted through an access hole in the side of the wooden case. This access hole is covered by an interior wooden sliding plate. A fuze well is located in another side of the wooden case and other fuze wells may be present in the bottom of the case. Two small holes for testing the circuit of the mine, after it has been laid, are located in one side of the wooden case.

Figure 145. Electric railway mine.

(2)

Fuze. When laid, the brass pressure cap of the electric railway mine fuze (figs. 146 and 147) bears on the under side of a railway tie and the antilifting plunger in the depressed position. The fuze case rests on a bakelite plate, which is fastened by screws to the top of the battery box. This fuze case consists of two half-cylinders separated by celluloid insultaion. One of these metal half-cylinders is wired to one terminal of the battery by way of the main detonator and the clockwork delay me-chanism, while the other metal half-cylinder is wired to the other terminal of the battery. These wired connections are made through to of the screws that fasten the fuze case to the bakelite plate. The two metal half-cylinders are covered by a bakelite cylinder with a brass cap. As shown in figure 147, the metal half-cylinder wired to the main detonator and the clockwork delay mechnism houses, and is in electrical contact with, a spring-loaded plunger. The other metal half-cylinder hou-ses a brass tube which is in direct electrical contact with it. Fixed on the brass tube is a square-section brass rod which projects into a vertical slot in the bottom part of the metal half-cylinder and prevents rotation of the brass tube. The brass tube is externally threaded at the top to take the contact strip, the brass collar, and the brass pressure cap. Inside the top part of the brass tube is an insulating liner and a spring which holds up the anti-lifting plunger. The bottom of this spring rests on a metal spind-le. The shanks of the metal spindle and the antilifting plun-ger are insulated. The spring surrounding the metal spindle controls the movement of the brass tube. It is held in place at the bottom by an ebonite plug.

Figure 146. Electric railway mine fuze.

b. Employment. This mine is laid under a railroad tie. If it is laid under a hollow steel tie, a nonmetallic pressure piece is provied between the top of the brass pressure cap and the tie.

c. Functioning (fig. 147).

(1)

Main circuits. The graduated disk on the head of the clockwork delay mechanism is marked with numerals up to 21, indicating the delay in days. The mine may be set to operate for delayed action in one of two ways.

(a)

The main circuit has a contact below the brass pressure cap which is closed when the brass pressure cap is depressed, so the contact strip makes contact with the spring-loaded plunger. A contact in the clock-work delay mechanism is closed at the expiration of the setting time. If the brass pressure cap is screw-ed up sufficiently against the under side of the tie, contact between the spring-loaded plunger and the contact strip will be made and the mine will be automatically detonated at the expiration of the set delay period.

(b)

If the circuit between the spring-loaded plunger and the contact strip is not closed at the time the mine is laid, the mine cannot function until the end of the set delay period, and then only by the action of a passing train which would depress the brass pressure cap and close the contact below the brass pressure cap.

(2)

Antilifting contact. The antilifting plunger is spring-loaded. If the mine is moved so this plunger is free to rise, the metal base will make contact with the under side of the brass pressure cap and complete a circuit which will set off the special electric detonator. A nonmetallic safety pin, inserted through the brass collar and the brass tube just below the brass pressure cap, is withdrawn after the mine is emplaced, but before the detonators are inserted. If a metal pin is inserted through the safe-ty-pin hole, it will make contact with the metal base of the antilifting plunger and complete the auxiliary circuit through the brass tube. In either case the mine will fire.

Figure 147. Cross-sectional view of the electric railway mine fuze and the firing circuit of the electric railway mine.

d. Installing and Arming.

(1)

Remove the lid and examine the contents to be sure that the batteries and the main charge are present.

(2)

Compare the wiring with figure 147 to asertain that the correct connections have been made.

(3)

Test the circuit through the two test holes in the side of the case.

(4)

Replace the lid.

(5)

Test the clockwork delay mechanism by setting it for a short delay period to be sure that it is functioning properly.

(6)

Dig a hole beneath a wooden railroad tie of sufficient size to permit vertical move-ment of the tie when a train passes over the mine installation.

(7)

Place the mine in the hole so that the brass pressure cap may be screwed up to bear firmly against the under side of the tie.

(8)

Set the clockwork delay mechanism for the desired delay and insert it in the mine through the access hole in the side of the wooden case.

(9)

Close the wooden sliding plate.

(10)

Remove the nonmetallic safety pin from the fuze.

Note. It is important that this mine be installed with a firm footing. If the soil in the hole is not sufficiently stable place boards, or similar material, so that the mine rests on a firm bearing surface.

e. Neutralizing.

(1)

Search for and neutralize any fuzes in the sides of the mine.

(2)

Expose the mine without moving it. Remove the special electric detonator, prying it out of its recess with a screw driver if necessary.

(3)

Slide out the cover plate covering the clockwork delay mechanism. With-draw the clockwork delay mechanism and main detonator together. To do this the wires should be cut one at a time.

Caution: Do not move the mine until the detonators have been with-drawn; do not insert a metallic pin in the safety-pin hole; do not allow the antilifting plunger to rise while the detonators are still in the mine; do not exert pressure on the brass pressure cap.