T. E. Lawrence, Demolitions Under Fire
The Royal Engineers' Journal, Vol. XXIX, No. 1, January 1919

We were interested in the Hejaz Railway, and spent nearly two years on it. The Turkish counter-measures were passive. They garrisoned each station (an average of 14 miles apart) with half a company, entrenched, sometimes with guns, and put in between the stations a chain of small entrenched posts, usually about 2000 yards. apart, and sited on small knolls or spurs within 200 yards of the railway, so that each post could see its neighbours and command all the intermediate line. Extra posts were put on one or other bank of any large bridge. The 15 or 20 men in the post had to patrol their section of line after dawn each day, and in the afternoon. There was no night activity on their part.

The Turks arrived at their system of defence after considerable experience of our demolition parties, but we were able, till the end of the war, to descend upon the railway when and where we pleased, and effect the damage we wished, without great difficulty. At the same time our ways and means had constantly to be improved. We began with small parties of ten or fifteen Beduins, and we ended with mobile columns of all arms, including armoured cars; nevertheless I believe that it is impossible for a purely passive defence, such as the Turkish, to prevent a daily interruption of the railway traffic by a decently equipped enemy. Railway defence, to be inviolable, would require a passive force, entrenched with continuous barbed wire fence, and day and night patrol, at a considerable distance from the line, on each side of it; mobile forces, in concentrations not more than 20 miles apart; and liberal air reconnaissance.

The actual methods of demolition we used are perhaps more interesting than our manners of attack. Our explosives were mainly blasting gelatine and guncotton. Of the two we infinitely preferred the former when we could get it. It is rather more powerful in open charges in direct contact, far better for indirect work, has a value of 5 to 1 in super-tamped charges, is quicker to use, and more compact. We used to strip its paper covering, and handle it in sandbags of 50 lbs. weight. These sweated vigorously in the summer heats of Arabia, but did us no harm, beyond the usual headache, from which we never acquired immunity. The impact of a bullet may detonate a sack of it but we found in practice that when running you clasp it to your side, and if it is held on that furthest from the enemy, then the chances are that it will not be hit, except by the bullet that has already inflicted a mortal wound on the bearer. Guncotton is a good explosive, but inferior in the above respects to gelatine, and in addition, we used to receive it packed 16 slabs (of 15 oz. each) in a wooden box of such massive construction that it was nearly impossible to open peacefully. You can break these boxes with an entrenching tool, in about four minutes slashing, but the best thing is to dash the box, by one of its rope or wire beckets against a rock until it splits. The lid of the box is fastened by six screws, but even if there is time to undo all of these, the slabs will not come out, since they are unshakably wedged against the four sides. I have opened boxes by detonating a primer on one corner, but regard this way as unnecessarily noisy wasteful and dangerous for daily use.

Rail Demolition. - Guncotton in 15-ounce slabs is convenient for rail cutting. The usual method of putting a fused and detonated and primed slab against the web is quick and easy, but ineffective. The slab cuts a six-in. section out of the line, leaving two clean fractured surfaces (Hejaz rails are of a mild Maryland or Cockerill steel). The steel chairs and sleepers are strong, and the enemy used to tap the broken rails again into contact with a sledge, and lay in a new piece whenever the combined fractures were important enough. New rails were ten metres long, but the line worked well on unbolted pieces two or three metres long. Two bolts are enough for a fish plate, and on straights the line will serve slow trains for a mile or two without fish plates, owing to the excellence of the chairs. For curves the Turks, after we had exhausted their curved rails, used short straights. These proved efficient even on 120-metre curves. The rate of repair of a gang 100 strong, in simple demolition is about 250 cuts an hour. A demolition gang of 20 would do about 600 cuts an hour.

A better demolition is to lay two successive slabs on the ballast beneath the bottom flange under the joint and fish plate, in contact with the line. This spoils the fish plate and bolts, and shortens each of two rails by a few inches, for the expenditure of two slabs and one fuse. It takes longer to lay than the simple demolition, but also takes longer to repair, since one or other rail is often not cut, but bent, and in that case the repair party has either to cut it, or to press it straight.

The best demolition we discovered was to dig down in the ballast beside a mid-rail sleeper between the tracks, until the inside of the sleeper (iron of course) could be cleared of ballast, and to lay two slabs in the bottom of the hole, under the sleeper, but not in contact with it. The excavated ballast should then be returned and the end of the fuse left visible over the sleeper for the lighting party. The expansion of air raises the middle of the sleeper 18 in. from the ground, humps the two rails 3 in. from the horizontal, draws them 6 in. nearer together, and warps them from the vertical inwards by the twisting pull of the chairs on the bottom outer flange. A trough is also driven a foot or more deep across the formation. This gives two rails destroyed, one sleeper or two, and the grading, for two slabs and one fuse. The repair party has either to throw away the entire track, or cut a metre out of each rail and re-grade. A gang of 100 will mend about 20 pairs an hour, and a gang of 40 will lay 80 an hour. The appearance of a piece of rail treated by this method is most beautiful, for the sleepers rise up in all manner of varied forms, like the early buds of tulips.

Simple demolitions can be lit with a 12-in. fuse. The fish-plate-flange type should be lit with 30-in. fuses, since the fragments of steel spray the whole earth. The 'tulips' may be lit with a 10-in. fuse, for they only scatter ballast. If, however, the slabs have been allowed to get into contact with the metal of the sleeper they will throw large lumps of it about. With a 10-in. fuse most of these will pass over the head of the lighting man who will be only 15 yards or so away when it goes off. To be further is dangerous. We were provided with Bickford fuse by Ordnance. The shiny black variety causes many accidents, owing to its habits of accelerating or smouldering. The dull black is better, and the white very good. Our instantaneous fuse has an amusing effect if lit at night among friendly tents, since it jumps about and bangs; but it is not good for service conditions. The French instantaneous fuse is reliable. Detonators should always be crimped on to ready-cut fuses, and may be safely carried in the pocket or sandbag, since great violence is required to set them off. We generally used fusees for lighting.

Speaking as a rule rail demolitions are wasteful and ineffective unless the enemy is short of metal or unless they are only made adjuncts to bridge-breaking.

A pleasant demolition, of a hybrid type, is to cut both rails, and turn them over, so as to throw them on their face down the bank. It takes 30 men to start this, but a small gang can then pass up the line, bearing on the overturned part, and the spring of the rails will carry on the reversing process, until you have done miles of it. This is an effective demolition with steel sleepers, since you wreck the ballasting. We tried it once on about 8 miles of a branch line, with a preponderance of spiked wooden sleepers, and it made such a mess of rails and sleepers that the Turks washed their hands of it.

The Hejaz line carried a minimum of traffic, so that there was no special virtue in destroying the points of crossing places.

Bridge Demolitions. - The lightness of traffic affected the tactics of bridge demolition also, since a single break was met either by transport or deviation. As with the rails however, the methods we used are perhaps more important than why we did it. Most of the bridges are of dressed limestone masonry, in 80 to 100-pound blocks, set in lime mortar. The average spans were from four to seven metres, and the piers were usually 15 ft. wide and 4 ft. 6 in. thick. It is of course better to shatter a bridge than to blow it sky-high, since you increase your enemy's labours. We found that a charge of 48 pounds of guncotton, laid against the foot of the pier on the ground, untamped, was hardly enough, and that 64 pounds was often a little too much. Our formula was therefore about ¹/₅BT² for guncotton charges below 100 pounds, untamped. In a pier 15 ft. broad, had the feet been marked off on it, we would have had no explosive between feet 1 and 3 and 12 and 15. The bulk would have been against 4, 5, and 10, 11, with a continuous but weaker band uniting and 10. Dry guncotton is better than wet for such work; gelatine is about 10 per cent. stronger for these open charges. With charges above 100 lbs. ¹/₆BT² or ¹/₇BT² is enough. The larger your object the smaller your formula. Under fire, the inside of the bridge is fairly safe, since enemy posts enfilade the line and not the bridge arches. It is however seldom leisurely enough to allow of tamping a pier charge by digging. When it is, a trench a foot deep is all that is possible, and this does not decrease a guncotton charge by more than 10 per cent. Gelatine profits rather more in proportion by simple tamping.

A quick and cheap method of bringing down the ordinary pier or abutment is by inserting small charges in the drainage holes that are usually present. In the Hejaz line these were in the splay of the arch, and a charge of 5 lbs. of gelatine, or 25 of guncotton, in these would wreck the whole line. The depth and small size of the drainage holes tamp the explosive to an extreme degree. Where the bridge was of many spans we used to charge alternate drainage holes on either side. In the ordinary English abutment where the drainage holes are small and frequent, it would be wise to explode several simultaneously by electricity, since the effect is much greater than by independent firing. Necklacing and digging down from the crown or roadbed are methods too clumsy and slow for active service conditions.

In North Syria, where we came to bridges of great blocks of basalt, with cement joints, we had to increase our charges for untamped work to ¹/₄ or even ¹/₃ BT².

We found guncotton most convenient to handle when we knotted it up into 30-slab blocks by passing cords through the round holes in the middle of the slabs. These large bricks are quick to lay and easy to carry. An armoured car is very useful in bridge demolition, to hold the explosive and the artist. We found in practice that from 30 to 40 seconds was time enough to lay a pier demolition charge, and that only one man was necessary. We usually used 2-ft. fuses.

Girder bridges are more difficult. In lattice bridges where the tension girder is below the roadway, it is best to cut both compression beams. If the tension girder is overhead, it is better to cut both tensions and one compression. It is impossible to do a bridge of this sort very quickly. We had not many cases, but they took ten minutes or more each. When possible we used to wedge the gelatine in the angles of meeting girders. The only quick way is to lay an enormous single charge on the top of the abutment and root it all away with the holdfasts. This may require 1000 lbs. of gelignite, or more, and a multiplicity of porters complicates things. I never blew up a plate girder.

Mining trains pertains perhaps more to operations than to engineering, and is, any way, a special study in itself. Automatic mines, to work on rail deflection always sounded better than they proved. They require very careful laying and to be efficient have to be four-charge compound. This involves electrical connection. The best mine action we had was made for us by Colonel R.E.M. Russell, R.E., and we were about to give it extended use when the enemy caved in.

The ordinary mine was fired electrically by an observer. It is an infallible but very difficult way of destroying hostile rolling stock, and we made great profit from it. Our standard charge was 50 lbs. of gelatine. Guncotton is very little use.

However mining is too large a subject to treat of. The army electrical gear is good, but the exploder seems needlessly heavy. By using a single strand insulated wire (commercial) we fired four detonators in parallel at 500 metres; army multiple-stranded insulated cables will fire two at 500 metres. In series I have never had occasion to fire more than 25 detonators (at 250 yards), but I see no reason why this number should not be greatly increased. The army electric detonators never failed us. A meter test might show that some of them were defective, but even the defective ones will fire on an exploder. It is usually unnecessary to insulate your joints. The exploder goes out of action quickly if knocked about in a baggage column, or slung on a trotting camel, so I usually carried two as reserve.

Note. The article was signed 'T.E.L.'