The subject of defence is treated of in F.S.R., 107-110, I.T., 125-135, and in Chapter VII., M.F.E., 1911. The duties required of the company commander and his subordinates are briefly defined by I.T., 132, to be similar to those they carry out in the attack. The whole spirit of the regulations is that the active Defence is merely a means to an end, viz., the ultimate assumption of the offensive, which may be carried out either by the same troops which have acted on the defensive or by fresh troops detailed for the purpose. In both cases the troops that have acted on the defensive must be ready to become the aggressors. Therefore, in training your men, you should keep this constantly in view and conserve a spirit of aggressive mobility. Men must not be allowed to think that once a position has been taken up and entrenched it is to be their location till fighting ceases; on the contrary, they should be encouraged to look for opportunities while still on the defensive, to occupy alternative positions which will make the task of the attacking enemy more difficult. Quickness in seizing and strengthening a position must be combined with mobility in leaving it to take up and strengthen a new one. Of course, the time available regulates the work that can be undertaken (M.F.E., VII. (2)); deep trenches and concealed head cover cannot be made with an enemy pressing in to assault, but the first requirement is the ability to choose positions that give a good field of fire and to strengthen them as thoroughly as the time available and the proximity of the enemy admit.