FIELD FORTIFICATION Field Fortifications, now more often spoken of as field de fences, are those which are constructed at short notice, with the means locally available, usually when the enemy is near at hand. Subject to the question of time, a very high degree of strength can be given to them if the military situation makes it worth while to expend sufficient labour. A century or more ago, the dividing line between permanent and field fortification was rigidly drawn, as a high masonry escarp surmounted by a rampart was essential to a permanent fortress and these could naturally not be extemporized. Works without masonry, in other ways made as strong as possible with deep ditches and heavy timbers, were known as semiperma nent, and were used for the defence of places which acquired strategic importance in the course of a war, but were not immedi ately threatened. The term field fortification was reserved for works constructed of lighter materials, with parapets and ditches of only moderate development. In modern fortification, if cupolas and deep revetted ditches were essential to permanent defences, the dividing line would be equally clear. But actually the use of our present means of construction, in conjunction with the defen sive power of modern fire-arms, makes it possible to extemporize in a very short time works having much of the resisting power of a permanent fortress. Further, such works can be expanded from the smallest beginnings; and, if the site is not too exposed, in the presence of the enemy.
Field fortification offers, as regards the actual constructions, a limited scope to the engineer; and a little consideration will show that its defensive possibilities were not greatly affected by the change from machine-thrown projectiles to those fired by rude smooth-bore guns. There is therefore nothing in the history of this branch of the subject that is worth tracing, from the earliest ages to about the end of the 18th century. One or two points may be noticed. The use of obstacles is probably one of the earliest measures of defence. Long before missile weapons had acquired such an importance as to make it worth while to seek shelter from them it would obviously have been found desirable to have some means of checking the onrush of an enemy physically or numeri cally superior. Hence the use by savage tribes, to this day, of pits, pointed stakes hidden in the grass, entanglements and similar ob stacles. In this direction the ages have made no change, and the most highly civilized nations still use the same obstacles on occasion.
Another use of field defences common to all ages is the protec tion of camps at night, where small forces are operating against an enemy more numerous but inferior in arms and discipline. In day light such an enemy is not feared, but at night his numbers might be dangerous. Hence the Roman practice of making each foot-sol dier carry a couple of stakes for palisades; and the simple defence of a thorn zariba used by the British for their camps in the Sudan. Palisades and trenches, abatis and sharpened stakes have always been used. Except wire, there is practically no new material. As to methods, the laagers of the Boers are preceded by the wagon forts of the Hussites, and those no doubt by similar arrangements of British or Assyrian war chariots ; and so in almost every direc tion it will be found that the expedient of to-day has had its fore runners in those of the countless yesterdays. The only really marked change in the arrangements of field defences has been caused not by gunpowder but by quick-firing rifled weapons. For that reason it is worth while to consider briefly what were the prin ciples of field fortification at the end of the 18th century. The field defences of the 19th century are transitional in character. Based mainly on the old methods, they show only faint attempts at adaptation to new conditions, and it was not till quite the end of the century that the methods now accepted began to take shape. The essential elements of fieldworks up to the time of the Penin sular War were command and obstacle; now they are protection and concealment.
The strength of a fortified line in the 18th century depended principally on its redoubts. Lines of shelter trenches had little power of defence at the time, unless they held practically as many men as would have sufficed to fight in the open. Obstacles on the other hand had a greater value against the inelastic tactics of the time than they have now. A good position therefore was one which offered good fire-positions for redoubts and plenty of facilities for creating obstacles. Strong redoubts which could resist determined assaults; good obstacles in the intervals, guns in the redoubts to sweep the intervals, and troops in formed bodies kept in reserve for counter-strokes—these were the essentials in the days of the smooth-bore.
The works of Torres Vedras have been chosen for illustration because they offer very good historical examples, and also because of the value of the critical remarks of Sir John Jones, who as a cap tain was the engineer in charge of their construction. At the same time, it must be remembered that they differ from ordinary field works in having an unusual degree of strength, plenty of time and civilian labour having been available for their construction. In this respect they approximate more to semi-permanent works, the main reason why they did not receive under the circumstances a greater development of ditch and parapet being that in addition to the large number of works required, much labour was expended in abatis, inundations, scarping hill-sides and constructing roads. The keynote of the period was thus that the redoubts were the most important features of lines of defence, and that they com bined physical obstacle and protection with good musketry and artillery positions. The value of concealment was not ignored, but it was as a rule subordinated to other considerations.
From 1877 to 1899 the efficiency of rifles and guns rapidly in creased, and radically affected the nature of protection required and instilled the lesson of the adaptation of works to ground. In the Boer War, and still more in the Russo-Japanese War, field defences not only exerted an increasingly important influence, but were themselves developed and modified until in the World War the technique of field fortification reached its height and assumed its present form. Modifications since 1918 have been in the direc tion of simplicity of design and elasticity of organization. (X.)