Active defence is maintained by flying columns, of strength and organisation suitable to the character of the enemy and the nature of the country. To these columns is confided the protection of certain areas, an end attained, not by inactivity, for the troops should be continually on the move, so that the enemy can never be certain when and where to expect them, but by a vigorous and energetic offensive in whatever directions an efficient service of intelligence reports hostile gatherings. The enemy's movements and projects must, in fact, be anticipated, rather than countered when in course of execution. DEFENCE OF A POST. When considering what steps are to be taken for the defence of a post, large or small, the maxim that the offensive is the best defence must be ever prominently before the mind. It follows that the first step, after a site has been selected, the water supply secured, and the usual measures for security taken, should be to set apart as many men as possible for offensive purposes, including reconnaissance. In other words, the strength of the reserve should be calculated from these premises, having due regard to the number of nights in bed required by the whole garrison; and the reserve should not be such men as may be left over after the requirements of passive defence have been fully satisfied. The next item should be the selection of a keep or citadel, where stores and ammunition can be placed, and where hospital, headquarters, and a central signalling and communicating station can be located. In this keep may be placed machine or other guns, if available, so arranged that they can sweep approaches to the post, and also, if possible, protect with fire the flanks of picquet stations. It will now be time to allocate, generally, the troops destined for guard and picquet duty. These arrangements may be primarily made from the interior of the post, its safety being the first consideration, though for reasons of sanitation the more space that can be given to troops and convoys the better. Picquets having been roughly allotted, the plan of defence should be regarded from the enemy's point of view, and the necessary changes made; and, finally, the bearings of the picquet positions should be taken from the keep, and routes to them cleared, in case they should require reinforcement by night. It should only be necessary to keep picquets at their full strength in night-time. By day the bulk of the men could fall back into the interior of the post, an arrangement which would at once facilitate water and food supply, and would also be advantageous from a sanitary point of view. The next duties will be to deal with the general sanitation of the post, and especially of the rest and convoy camps, to mark out the latter, and to secure their policing.