6. Study the ground and direct the advance in such a way as to take advantage of all available cover and thereby diminish losses. 7. Never deploy until the purpose and the proper direction are known. 8. Deploy enough men for the immediate task in hand; hold out the rest and avoid undue haste in committing them to the action. 9. Flanks must be protected either by reserves, fortifications, or the terrain. 10. In a decisive action, gain and keep fire superiority. 11. Keep up reconnaissance. 12. Use the reserve, but not until needed or a very favorable opportunity for its use presents itself. Keep some reserve as long as practicable. 13. Do not hesitate to sacrifice the command if the result is worth the cost. 14. Spare the command all unnecessary hardship and exertion. MISCELLANEOUS. _MACHINE GUNS._ 537. Machine guns must be considered as weapons of emergency. Their effectiveness combined with their mobility renders them of great value at critical, though infrequent, periods of an engagement. 538. When operating against infantry only, they can be used to a great extent throughout the combat as circumstances may indicate, but they are quickly rendered powerless by efficient field artillery and will promptly draw artillery fire whenever they open. Hence their use in engagements between large commands must be for short periods and at times when their great effectiveness will be most valuable. 539. Machine guns should be attached to the advance guard. In meeting engagements they will be of great value in assisting their own advance, or in checking the advance of the enemy, and will have considerable time to operate before hostile artillery fire can silence them. Care must be taken not to leave them too long in action. 540. They are valuable to a rear guard which seeks to check a vigorous pursuit or to gain time. 541. In attack, if fire of position is practicable, they are of great value. In this case fire should not be opened by the machine guns until the attack is well advanced. At a critical period in the attack, such fire, if suddenly and unexpectedly opened, will greatly assist the advancing line. The fire must be as heavy as possible and must be continued until masked by friendly troops or until the hostile artillery finds the machine guns. 542. In the defense, machine guns should be used in the same general manner as described above for the attack. Concealment and patient waiting for critical moments and exceptional opportunities are the special characteristics of the machine gun service in decisive actions. 543. As part of the reserve, machine guns have special importance. If they are with the troops told off to protect the flanks, and if they are well placed, they will often produce decisive results against a hostile turning movement. They are especially qualified to cover a withdrawal or make a captured position secure.