A commander may desire to pin the enemy to an attack upon a fortified position, garrisoned by a portion only of his force, while he detaches another (and probably greater) portion to attack the enemy from an unexpected quarter. An outstanding example of this form of action is exhibited in the Battle of Chancellorsville (May 2-3, 1863), where Lee kept at bay Hooker's army of 90,000 with one-third of his force and detached Stonewall Jackson with 30,000 men to attack the Federal rear. Action of this kind is peculiarly effective, but it requires a secrecy which modern aircraft would almost certainly unveil, and if the manoeuvre failed to escape observation it would probably result in disaster both to the retaining force and to the detached troops.
A different form of the combination of defence with manoeuvre is the Defensive-Offensive battle, with examples of which the history of Warfare is amply supplied—Marengo, Austerlitz, and Waterloo being typical battles of this nature. In this form of defensive action a commander invites the enemy to attack a well-chosen position, and after exhausting the enemy's strength and holding up the assault, the commander passes from the guard to the thrust and overwhelms {77} the exhausted foe by an irresistible and sustained counter-attack with all the means at his disposal.
A position is sometimes occupied as a matter of necessity, sometimes merely as a matter of tactical prudence. At Nachod (June 27, 1866) the Prussian Advanced Guard hurriedly established a defensive position and kept at bay the whole Austrian Army, while the Prussian Army emerged in security from a defile and manoeuvred into battle array. The Pass of Thermopylae was occupied in B.C. 480 by 1,400 Greeks under Leonidas, King of Sparta, to withstand the Persian hosts of Xerxes, and although the Greek force was destroyed by an attack from the rear (through the disclosure of a secret path by a renegade in the Persian service), the resistance offered to the "invincible" Persians emboldened the Greeks in their future encounters, and led to the ultimate defeat of the invaders. According to the legendary history of Rome, Horatius Cocles and two companions defended the Sublician Bridge over the Tiber against Lars Porsena and the whole army of the Etruscans. This legendary heroism was equalled or surpassed during the Second Battle of the Somme (March 21, 1918). "The bridges across the Crozat and Somme Canals were destroyed, though in some cases not with entire success, it being probable that certain of them were still practicable for infantry. Instances of great bravery occurred in the destruction of these bridges. In one case, when the electrical connection for firing the demolition charge had failed, the officer responsible for the destruction of the bridge personally lit the instantaneous fuse and blew up the bridge. By extraordinary good fortune he was not killed" (Sir D. Haig's Dispatches). At Rorke's Drift (January 22, 1879) a force of 80 other ranks of the 24th Regiment, under Lieutenants Chard and Bromhead, with about 40 hospital cases, drove off the repeated attacks of 4,000 Zulus, part of Cetewayo's army which had surprised and annihilated the garrison {78} at Isandhlwana earlier the same day. An astounding feat of arms was performed by a small body of troops during the withdrawal of the British Army in face of the overwhelming German attack at the Second Battle of the Somme. A detachment of about 100 officers and men of the 61st Brigade, 20th Division, was detailed to cover the withdrawal of their division at Le Quesnoy (March 27,1918). Under the command of their Brigade-Major (Captain E. P. Combe, M.C.) the detachment successfully held the enemy at bay from early morning until 6 p.m., when the eleven survivors withdrew under orders, having accomplished their task.
There are many instances of the occupation of an area for an actual or potential tactical purpose. Before the Battle of Salamanca (July 22, 1812) a Spanish force had been detached by Wellington to cover a ford of the River Tormes by occupying the castle of Alba de Tormes, but the force was withdrawn without Wellington's knowledge, and Marmont's defeated army retired unmolested over the ford to the fortress of Valladolid. In the campaign of 1814, Napoleon placed a garrison of 1,200 in the Fortress of Soissons, but on March 3,1814, the garrison capitulated without exhausting all the means of defence as the regulations of War ordain, and the bridge at Soissons enabled Blücher and Bülow to unite their forces across the River Aisne. In the Waterloo campaign, Wellington stationed 17,000 men at Hal and Tubize, 8 miles from his right on the field of battle at Waterloo, to repel a possible turning movement and to form a rallying point if his centre was broken, and with 67,000 men took up a position astride the Nivelle-Brussels and Charleroi-Brussels roads which met at Mont St. Jean. He was deprived of the services of this detachment and modern criticism has been directed against this disposition of his forces. It is, however, permissible to suggest that the security of his right flank, and the possession of a rallying point, inspired him with the confidence which enabled him to {79} withstand the sustained attacks of Napoleon until the arrival of Blücher's corps permitted him to overwhelm his adversary.
A further form of defensive action is the occupation of a series of extemporised positions and the orderly withdrawal to a further series before the actual assault of the enemy, resistance being combined with manoeuvre for the purpose of delaying the enemy's advance or of holding up his pursuit. Delaying action of this kind is commonly employed in rearguard fighting, when the object to be gained is time rather than position, and the offensive action of the defender is limited to local counter-attacks at favourable or desperate moments. But the guiding principle in all defensive operations, including delaying action, must be that "when an enemy has liberty of manoeuvre, the passive occupation of a position, however strong, can rarely be justified, and always involves the risk of crushing defeat" ("Field Service Regulations," vol. ii. (1920)).
THE OFFENSIVE SPIRIT.—Although there are many forms of defensive action the soul of the Defence in every case is a vigorous offensive spirit. In the Active Defence, the Decisive Counter-Attack, ending in the overthrow of the enemy, is the manoeuvre originally in view when the defensive rôle is adopted. In the Passive Defence against superior numbers. Local Counter-Attacks end with the recapture of a tactical point or the repulse of a determined assault, and in the Delaying Action they overwhelm by surprise fire or assault a detached force which has advanced with such rapidity as to enable the defenders, without undue risk, to cut off and annihilate the isolated enemy body. Whatever the tactical situation, it is by the vigour of the offensive spirit alone that success may be achieved in the face of a determined enemy.
MODERN WARFARE.—In modern warfare the defensive position plays a part of increasing importance, owing {80} to the great power conferred on the defence by modern armaments. "Machine guns and barbed wire permit the rapid organisation of defensive points of a value which cannot be disputed. In particular, they have given to a trench, or to a natural obstacle, a solidity which permits a front to be extended in a manner unsuspected before this war; they permit the prompt consolidation of a large system that is easy to hold" (Marshal Foch). "The modern rifle and machine gun add tenfold to the relative power of the Defence as against the Attack. It has thus become a practical operation to place the heaviest artillery in position close behind the infantry fighting line, not only owing to the mobility afforded by motor traction but also because the old dread of losing the guns before they could be got away no longer exists" (Marshal French). It is thus possible to hold the forward positions of a highly organised defensive system with a minimum of exposure to loss, the extra strength of the position counterbalancing the reduction in numbers, but a preference for defensive action of this kind may generally be regarded as an admission that a victorious outcome of the campaign is not anticipated at the time of its adoption in the theatre in which it is employed. "It is of paramount importance that in those parts of a theatre of operations where a commander aims at decision a war of movement must never be allowed to lapse into position warfare so long as a further advance is possible. Position warfare can never of itself achieve victory" ("Field Service Regulations," vol. ii. (1920)). However strong entrenchments may be they will not defeat the adversary's main armies, nor can they withstand indefinitely the attacks of a determined and well-armed enemy. It is scarcely even probable that an army behind entrenchments can by that means alone inflict such losses on its assailants as will enable the initiative, or liberty of manoeuvre, to be regained and the assailant's main armies to be defeated. The operations on both sides {81} are in the nature of a siege, and however prolonged the siege, the advantage will be gained in the long run by superiority of aggressive action in the air and over and under the ground. In addition to the absence of opportunity for the grand offensive there are two further points of difference between defensive action in Position Warfare and the defence in a War of Manoeuvre. The first of these is the inevitable absence of flanks to be assailed, as the operations necessitate a connected line of strong points from sea to sea, or from the sea to the impassable barrier of neutral territory. Mounted troops are therefore doomed to inaction in their most important sphere, until the lines have been breached and the enemy is forced to retreat, and the opportunities for delivering flank attacks are meanwhile confined to the infantry, and will be due to irregularities in the alignment of the strong points, upon which enfilade fire may be brought to bear. The second point of difference is the abundance of time at the disposal of commanders for developing and rehearsing elaborate systems of attack and defence, and for obtaining detailed plans of the hostile works, through continuous reconnaissance by the Air Service. In most countries there must be, of necessity, a prolonged period of inactivity on both sides in a Position War, owing to the severity of winter conditions, or to the occurrence of the rainy season, and during that period it will seldom be possible to penetrate the enemy's main defences on such a scale as to bring about the grand offensive. But this is a period of inactivity in appearance rather than in fact, for no defensive system is ever perfect, no strong point but needs further consolidation, new trenches are constantly constructed or improved, and fresh areas are covered with wire entanglements. Guns of all calibres, underground mines and light mortars are ever at work, demolishing, wounding, and killing, while lachrymatory and asphyxiating shell-fire is to be expected at all times. On a smaller scale, snipers on both sides have a daily bag, and {82} observers are ever at their posts noting every change, however insignificant, and every new piece of work; "listening posts" are detecting hostile plans, while patrols are collecting information and raiding parties are reconnoitring, destroying defences, and inflicting losses, it being the first principle of a raid that it should result in greater losses to the enemy than to the troops which carry it out.
ENTRENCHMENTS.—Entrenchments have been employed in the defence from the earliest times. The Roman walls in Britain, the Great Wall of China, the earthworks in the Russian War of 1854-1855, in the American Civil War of 1861-1864, in the Russo-Turkish War of 1878, and the Russo-Japanese War of 1904-1905 are notable examples. But in no war previous to that of 1914-1918 have they played so important a part.
One of the most famous series of entrenchments in previous wars were those constructed in 1810 by Colonel R. Fletcher, of the Royal Engineers, at Torres Vedras. These fortifications extended for 50 miles and contained 126 closed works, mounting 247 guns, and behind these lines Wellington amassed stores and reinforcements until the retreat of Masséna enabled him to resume the initiative. In front of these lines everything that could support the French armies had been removed; behind them Wellington's forces were well provided in every respect. On October 10, 1810, Masséna was confronted by the entrenchments, the existence of which had been kept a profound secret, while their strength prevented them from being carried by assault. Before the end of October a Portuguese spy wrote to Wellington: "Heaven forgive me if I wrong the French in believing they have eaten my cat" (Napier). During the night of November 14-15, Masséna broke up his camp and withdrew. But it was not the lines of Torres Vedras which won back the Peninsula. Spain and Portugal were saved by the bold march northwards {83} to Vittoria. "In six weeks Wellington marched, with 100,000 men, 600 miles, passed six great rivers, gained one decisive battle, invested two fortresses, and drove 120,000 veteran French troops from Spain" (Napier).
DEFENSIVE SYSTEMS.—"Whether it is the intention of the commander to resume the offensive at an early date or whether it is likely that the defensive system will be occupied for a considerable period, the principles on which the construction of all defences should be undertaken are the same. All defensive systems should be planned from the outset in such a way that they can easily be adapted to the requirements of a prolonged defence. The ground must be thoroughly reconnoitred and should at the first be divided into a series of tactical posts and defended localities. These posts should be self-supporting, but should be so sited that the garrisons mutually support each other by fire. The gaps between the posts must be covered by the fire of the garrison of the posts, and machine guns may also be sited to bring fire to bear from positions in rear and to the flanks" ("Infantry Training, 1921"). This principle must govern the choice of the position to be defended as well as the organisation of the position for defence, and troops detailed for the defence of an area must continue to improve the defensive arrangements in that area until such time as the offensive is resumed.