ABOVE all things we must distinguish thick tangled and impassable forests from extensive woods under a certain degree of culture, which are partly quite clear, partly intersected by numerous roads.
Whenever the object is to form a defensive line, the latter should be left in rear or avoided as much as possible. The defensive requires more than the assailant to see clearly round him, partly because, as a rule, he is the weaker, partly because the natural advantages of his position cause him to develop his plans later than the assailant. If he should place a woody district before him he would be fighting like a blind man against one with his eyesight. If he should place himself in the middle of the wood then both would be blind, but that equality of condition is just what would not answer the natural requirements of the defender.
Such a wooded country can therefore not be brought into any favourable connection with the defensive except it is kept in rear of the defender's army, so as to conceal from the enemy all that takes place behind that army, and at the same time to be available as an assistance to cover and facilitate the retreat.
At present we only speak of forests in level country, for where the decided mountain character enters into combination, its influence becomes predominant over tactical and strategic measures, and we have already treated of those subjects elsewhere.
But impassable forests, that is, such as can only be traversed on certain roads, afford advantages in an indirect defence similar to those which the defence derives from mountains for bringing on a battle under favourable circumstances; the army can await the enemy behind the wood in a more or less concentrated position with a view to falling on him the moment he debouches from the road defiles. Such a forest resembles mountain in its effects more than a river: for it affords, it is true, only one very long and difficult defile, but it is in respect to the retreat rather advantageous than otherwise.
But a direct defence of forests, let them be ever so impracticable, is a very hazardous piece of work for even the thinnest chain of outposts; for abattis are only imaginary barriers, and no wood is so completely impassable that it cannot be penetrated in a hundred places by small detachments, and these, in their relation to a chain of defensive posts, may be likened to the first drops of water which ooze through a roof and are soon followed by a general rush of water.
Much more important is the influence of great forests of every kind in connection with the arming of a nation; they are undoubtedly the true element for such levies; if, therefore, the strategic plan of defence can be so arranged that the enemy's communications pass through great forests, then, by that means, another mighty lever is brought into use in support of the work of defence.