Machine guns, by reason of their concentrated fire and shallow beaten zone, are peculiarly suited for compelling troops to deploy at long range. They are also suited for quickly taking up a defensive position, and, when mobile, can instantly cease fire and move off in a few moments with considerable rapidity. Their power for suddenly developing an intense fire will enable them quickly to overwhelm an enemy caught “emerging from a defile or difficult country.” It would appear therefore that the machine guns are far more fitted than infantry to perform the duties of a rear guard as quoted above. “The first consideration in selecting a position for the artillery is that it shall be able to open fire on an enemy at long range, and thus compel his infantry to assume an extended formation at the greatest possible distance. The second is that it should be possible to withdraw without difficulty.”[33] When the infantry arrive within effective rifle range of the artillery, the latter will be compelled to retire, especially if the former are supported by cavalry. This will also be the moment when the infantry will require to retire to a fresh position in rear. Machine guns that have been well concealed, or which have taken up fresh positions in good cover in rear of the infantry line, should be able to unmask and by their fire hold off the enemy until both guns and infantry have effected their retreat. The facility with which they can traverse and sweep widely extended lines, and instantly concentrate fire on any portion of it, make them of great service in covering a retirement at effective range, as they can render the hottest fire ineffective and aimed fire impossible for a short time. Machine guns with a rear guard must be prepared to work from place to place with great rapidity, and for this purpose they must arrange to bring the gun horses close up to their fire position. Alternative positions are essential, but must be reached under cover and unobserved by the enemy. Sections will act independently, using their guns in mutual support; but the retirement of one section may often afford another the opportunity, from a well-chosen position on a flank, to surprise the enemy from close range as they press forward to occupy the abandoned position. A ruse that may sometimes be successful where guns are really well concealed is to bring up the gun horses and retire at a gallop by a pre-arranged signal all along the position, but leaving one gun of each section still in position but flat on the ground, where it will be completely concealed even from glasses. This is almost certain to draw a hot pursuit, especially if the artillery and infantry have retired previously, and if fire is reserved till close range a severe check may be administered to the enemy. “Skilfully laid ambushes will cause the enemy to move with caution in pursuit.”[34]