5
Plate I.
The ley el of the ground in this instance forms the banquette or step to fire from.There will he about 5 cubic yards in 6 running feet of breastwork, and as there aresupposed to be a double number of men at work, it ought to be finished in two orthree hours.*
g. This mode of executing work may also be adopted with advantage in othercases when time is an object, and there are plenty of hands, or when it is of im-portance to strengthen and give height to breastworks in particular situations. Butas far as this profile is concerned, it is to be observed, that it would afford cover toan enemy when he got at it, without opposing any impediment to his advance, whichit is always very desirable to avoid.
h. Should the ground be rocky or very hard, as in a road or street, cover mayperhaps be more expeditiously obtained by raising a breastwork from rubbish ormaterials brought to the spot in baskets, sand-bags, or barrows, than in attempting tosink at all. Different expedients are shewn in Plate II. figs. 11 and 12.
i. Having thus far detailed the most expeditious modes of providing cover for men,it may now be worth while to consider whether in securing that advantage for thedefenders, you cannot at the same time add another, in opposing an obstacle to anenemy, by excavating a ditch va front of the breastwork in place of making a trenchin rear of it. A ditch to stop people at all, should be at least 8 or 9 feet broad, and6 or 8 feet deep; in more Permanent Works it would of course be considerablymore.
k. Fig. 5 shews the general dimensions which such a profile might have. Theditch, it will be observed, is of a triangular form, the area of which, for calculating thequantity of earth to he moved, will be found by multiplying its breadth by one-halfits depth, that is, 9 feet by 4 feet, which gives 36 superficial feet; and that multipliedagain by the length of the portion each man has to execute, (w'e will here say 4 feet,as the breadth is considerable,) will be 36 x 4 = 144 cubic feet, or about 5 cubicyards in each portion of 4 feet; which, considering the increased labour arising froma greater depth than has hitherto been contemplated, would not probably be com-pleted in less than six hours by the same workmen. Some spare men, probably equalto one-half the number employed in the ditch, would also he required for rammingthe earth, and forming the breastwork. Thus on 100 feet in length there would betwenty-five men working in the ditch, and twelve additional, making in all thirty-seven; whilst in the common trench-work, which has hitherto been under con-sideration, only about seventeen workmen have been shewn to be necessary for every100 feet.
l. A profile, such as that now under discussion, therefore requires not only longertime to execute, but double the number of men; and it would not seem advisable toundertake it, unless there were a reasonable probability of its being completed beforean attack could be made; for if an enemy came upon it when in an unfinished state,it would be almost useless, and the labour, which if otherwise applied would havesecured at least good cover, would thus be thrown away. Still, however, the advan-tages it offers should not be lost sight of in situations where a determined stand is tobe made, and on very accessible points, or to shut up roads or streets, &e., even if therest of an intrenchment were differently arranged. As far as the means of resistanceis concerned, it is obviously of more advantage to have a ditch in front of a breast-
* When from circumstances the depth of a trench or ditch is very limited, the probable time itwill take to form a breastwork out of them, is more readily determined by estimating the content ofthe mass to be raised, than the excavation, as in the preceding cases, because the breadth of the latterwill probably be irregular.