PRELIMINARY CONSIDERATIONS, DEFINITIONS, ETC.
9. By a regular siege is meant a systematic and more or less deliberate attack upon a fortified place, in which the besieger aims to invest the place and capture its fortifications in succession by regular approaches, beginning with the most advanced and ending only with the reduction of the innermost keep and the surrender of the garrison.
The successive steps of a siege are usually the following:
The investment.
The artillery attack.
The construction of parallels and approaches.
Breaching by artillery or mines.
The final assault.
The introduction of modern breech-loading rifled guns, howitzers and mortars, rapid-fire and machine guns, and magazine small arms has brought with it the need of a higher grade of mechanical skill and improved machinery for making the ordinary repairs. This imposes upon both attack and defence the necessity for providing machine shops and tools fitted for work of this kind, with the steam power required to drive them. In connection with these, steam sawmills and other simple wood-working machines should be provided, as well as all other available labor-saving appliances which can be used to lighten the labor of the troops.
Portable tools, such as picks, shovels, crowbars, rammers, axes, hatchets, bill-hooks, gabion-knives, hammers, saws, carpenters', joiners' and blacksmiths' tools, etc., etc., must be provided.
10. The principal special tools and appliances used are the following, viz.: sap-forks, sand-bag forks, scrapers, sap-shields, measuring-rods of various lengths, pocket compasses with attachments for fastening them to measuring-rods, tracing-lanterns, dark and ordinary lanterns, tracing tape or cord, tracing pickets or stakes, fascines, gabions, hurdles, sand-bags, blindage and gallery frames and sheeting, etc., etc.
The sap-fork and sand-bag fork ([Pl. I], Figs. 1 and 2), about 4½ and 4 feet long, respectively, have steel heads with three and four prongs, as shown in the figures, those of the sap-fork being sharp and those of the sand-bag fork blunt.
They are used for handling and placing gabions, fascines, and sand-bags in position when, without their use, the sappers' arms would be exposed to fire.
The scraper ([Pl. I], Fig. 3) is a large hoe, of about the dimensions given in the figure, used for levelling off the surface of parapets, etc.
The sap-shield, introduced by the English ([Pl. I], Figs. 4 and 6), is a flat plate of mild steel 3 feet 6 inches by 1 foot 9 inches × ¼ inch, with two handles on its back as shown. Total weight, about 80 lbs.
It may be used as shown in the figure, and sometimes by small parties as a body-shield in such operations as blowing in gates, etc., etc.
Measuring-rods of rectangular cross-section, straight and divided into feet and inches, are needed for special purposes; but the ordinary rods are cut from round brush wood and to the length required.
Tracing-tape is usually a white tape, about 1½ inches wide, in lengths of 150 feet, marked at equal intervals, usually 5 feet, by short pieces of tape sewed to it. A loop of strong cord is fastened to each end. For convenience in use it is ordinarily rolled into a ball.
Tracing-pickets are about 18 inches long and one inch in diameter. To make them visible in a dim light the bark is removed from them. Ordinary pickets are usually 3½ or 4 feet long, 1½ to 1¾ inches in diameter, sharpened to a triangular point.
The tracing-lantern ([Pl. I], Fig. 5) is a dark lantern with a reflector arranged to throw a light vertically downward.
The other tools, materials, and appliances above mentioned, not of the ordinary commercial patterns, are described in Field Fortifications and Military Mining, q.v.
CHAPTER III.
TRENCHES, APPROACHES, PARALLELS, SAPS, SPLINTER PROOFS, AND PASSAGE OF THE DITCH.
11. Trenches.—A military trench consists of a ditch and embankment affording cover from direct fire. Trenches are used for approaches (or boyaux), parallels, and communications with magazines, etc.
12. Parallels are trenches which take their name from the fact that they usually are located on lines approximately parallel to the general front of attack. In a regular siege at least three and frequently a greater number of parallels are used. The exterior one, which is first made, is known as the first parallel, the next one as the second parallel, and so on. They are used to cover the part of the besieging force known as “the guard of the trenches,” which protects the men making the approaches, etc., and also as “places of arms” for assembling troops for assault or for other purposes.
The trench of a parallel is usually 10 feet wide at the bottom and 4 feet deep, finished on the reverse with a slope and on the front with two steps and a berm, with treads of 18 inches and rises of 15-18 inches ([Pl. I], Figs. 7 to 13).
The parapet of the parallel should not be higher than 4 feet 6 inches. Its upper surface, particularly in the second and third parallels, should be made approximately plain with a scraper, and its interior slope should be finished and if necessary revetted, so as to afford a good infantry-fire. To allow the troops to move out to the front in line, portions of the interior slope should be cut into steps of not more than about 18 inches rise, and be revetted with fascines or other materials ([Pl. I], Figs. 12 and 13). These portions should be 25 or more yards long and near the approaches. If a general assault is to be made, the parallels must be similarly arranged for the necessary length of front.
13. Approaches are trenches leading up toward the fortification on the front of attack; they connect the parallels and give protection to the besiegers in moving back and forth. To avoid enfilading fire they usually run in zigzags ([Pl. VIII], Figs. 80 and 81) across the capitals of the work, with branches seldom exceeding 100 yards in length at the first parallel, and growing continually shorter as they approach the work. Each branch is so directed that its prolongation will pass from 30 to 40 yards outside the most advanced position within effective range held by the defence. At each turning-point of the zigzag the more advanced branch is prolonged from 10 to 20 or more yards to the rear, to cover the angle of the approach. These returns are also useful for storing trench material, etc.
After the return is completed the sharp angle in the trench is rounded off to allow gun-carriages, etc., to make the turn.
Approaches are usually 4 feet deep, 9 to 12 feet wide at bottom, with slopes in front and rear as steep as the earth will stand, and have a rough parapet not less than 4½ feet high, separated from the trench by a berm of 18 inches, or more if necessary ([Pl. VIII], Fig. 82). When drainage requires it, as it very frequently does, the bottom of the trench is sloped from front to rear about 6 inches; a ditch cut along the reverse slope, discharging into the drainage ditches of the vicinity, or into drainage pits excavated in rear of and outside the approaches. These may be lined with a gabion to prevent their sides falling in.