APPROACHES, Military. The succes ors of Vauban followed up, as far as practi cable, the methodical stages in conducting the attack founded upon his long experience, and which consisted in a single or a double con nected attack: approaching the points assailed by as many lines of communication, directed upon them, as circumstances seemed to de mand, and protecting these approaches by three continuous main lines of trenches, termed the parallels, and severalrtions of parallels, termed demi-parallels, between the sec ond and third parallels, all of them very care fully placed so as to be in good tactical rela tions to one another.
The approaches were usually run in zigzag directions toward the salients of the defenses, crossing the lines of the capitals of these salients, the front of each approach gradually contracting as it was advanced toward the salient, and each boyau- of the approach re ceiving such a direction as not to expose it to an enfilading fire from any point of the de fenses within cannon-range. In addition to the communications between the parallels, two or more lines of approaches were run, from the positions selected for the depots of the trenches, to points of the first parallel con venient for the supplies for this and the other lines of works. These were also usually run in the direction of the capitals of some two or more of the salients.
Besides giving the boyaux directions un favorable to an enfilading fire from the de fenses, each one is extended some 12 or 13 yards back, to the rear of the one behind it, so that should the besieged endeavor to take up a temporary position, exterior to his main de fenses, each boyau would still be covered by the portion of the one in advance of it run to the rear, not only from an enfilading but from any slant reverse views, except from points so far beyond the defenses as to make their temporary occupation very perilous to the besieged, from their exposure to open assaults.
The positions given to the approaches along the capitals are not obligatory; but will gen erally be found to offer more advantages than any other that could be given them on ground entirely unobstructed. In the first place, the capitals are the shortest lines from the parallels to the salients of the defenses. In the second, running the boyaux across the capitals, and gradually diminishing the extent of their front, the entire approach will be better flanked by the fire of the parallel in its rear; will be in a position to receive but little if any of the fire which is delivered from the two faces of the salient upon which it is run; will be out of the line of fire of the batteries enfilading these two faces; and will usually be in the most favorable position to defile each boyau from the fire of the besieged.
The front occupied by each approach will depend upon the length given to each boyau. As a general rule, the boyau should not receive a greater length than 100 yards, in order not to expose too long a line to tempt the besieged to enfilade it, and the approach may be started at the first parallel with a front of 60 yards, which should be gradually narrowed, so as to have a front of about 30 yards at the position of the third parallel.
Prior to the great European War, one of the most tremendous combinations of approaches in the history of war was at the siege of Sebas topol. It comprised the digging of no less than 70 miles of sunken trench, and the employment of 60,000 fascines, 80,000 gabions and 1,000,000 sand-bags to protect the men working in the trenches and at batteries. See SIEGE.