The principles of the oblique attack on an enemy's flank may be farther illustrated, by considering the ef fects of an attack directed against an army while march ing. To attack an army on the march, indeed, is advan tageous, for the same reason that it is desirable to en gage an extremity of an enemy's line ; because the army attacked on the heads of its columns is placed, relatively to its opponent, in the same situation with that assailed in flank. This is demonstrated by the following figure.
Supposing both armies in line ; B will be found to be attacked by a perpendicular line, with one of its extre meties outflanked, in the same manner as the heads of its columns would be, if the army were on march.
Both manceuvres produce similar advantages ; which are, that the army attacked can only bring its battalions successively into action, while the attacking force, press ing forward with vigour, is enabled to overthrow them one after another. In order to secure this result, it is not enough to attack an army on march, but the corps A must, besides, move in a corresponding direction ; that is, by prolonging the march horizontally, if the advance of the hostile columns be perpendicular, and prolonging the perpendicular movement, if that of the enemy be horizontal. The object of these directions must be, to present a whole line to the head of a column, and, con sequently, to a single extremity of the enemy's line. It is obvious, that if the heads of two hostile columns were to meet in similar directions, and began reciprocally to deploy, the consequence would produce a parallel order of battle, and a shock between two equal fronts, totally levoid of combinations.
The army A, marching in two columns, is met by B, moving in a similar direction, (both perpendicularly) the first will immediately deploy, for fear of being at tacked ; and if the second do not instantly perform the same evolution, it will be defeated, as appears from the former figure. A, consequently, will form tke line CC, B the line DD. But this reproduction of parallel fronts, of battalion opposed to battalion, unquestionably results from incapacity on the part of the commanders. The armies, thus drawn up, may destroy each other, without either gaining a decisive advantage ; and which ever gains the victory, it will not be owing to the skill of the general.
An army, therefore, which is attacked on the march, will immediately endeavour to form an angle ; or, in other words, the leading brigade of the columns will instantly deploy; and this deployment being either to the right or left of the columns, will constitute an angle or notence,as may be seen by the following figure.
A forms the advanced guard, or the head of the co lumns B ; if it be attacked by the enemy, it will deploy to either hand, according to the direction of the attack, and occupy the dotted lines, which form an angle or potence with respect to the columns. This manceuvre is necessary to oppose the first efforts of the enemy C. But being secure from immediatee danger, does it fol low that the army must imitate the movement of the leading brigade, and restore the parallel order ? At first sight, the manceuvre appears and it is most commonly the refuge of generals possessed of inferior talents ; yet it is not, on that account, the most advisable. If it be proved that an attack upon a flank is most appro priate, why should not an army, of which the vanguard, or the brigade on the flank happens to be engaged with the enemy in front, endeavour in its turn to gain the flank of the assailant, and exchange defensive for offen sive measures—a probable defeat for almost certain vic tory ? Nothing can prevent a commander, when attacked in this manner, from ordering the brigade in action to defend its post inch by inch, and to retire gradually upon another intermediate brigade, placed echelon•wise in its rear ; and while these are engaged, he can change the direction of his columns, by facing the platoons to the right or left, and move by their flanks, until he has in his turn outfi mked the enemy's line. (See Plate CCCLXXX111. Fig. 42 ) The platoons nearest the enemy will prolong their file movement considerably more than at a greater dis tance behind, the latter gradually taking less ground ; so that the last forms the pivot, or has only to continue its original perpendicular march. From this disposition an oblique formation will result, which outflanks the enemy, and prevents his pressing forward upon the re treating brigade, because, in consequence of the new order of battle, he is in danger of being himself attacked to great disadvantage, if the enemy operates with vigour and unison. .The manoeuvre is both more bimple and more rapid in the execution. It offers the singular ad vantage of placing the whole army upon an extremity of the enemy's line ; while the change of front, if per mitted to be performed, only restores the parallel order of battle. If this manceuvre, of an open column mov ing by files to a flank, appear complicated, others may be substituted in its stead, provided they are conducted on the principle of throwing the mass of the forces on the flank of the enemy.