Though experience is the only true test of a system of tactics, the foundations of the tactics suitable to any particular weapon are not based on experiences, but on the limitations of the weapon, that is on its powers, and on the fundamental principles of war. Further than this, if the weapon concerned is to be employed in co-operation with other weapons, the powers of these other weapons must also be considered, so that all the weapons to be employed may, so to speak, like a puzzle, be fitted together during battle to form one united picture.
In thinking out a tactics for tanks, the first factors to bear in mind are the powers of the machine, which may be summarised in three words: “penetration with security.” Heretofore fronts had remained to all intents and purposes inviolable to direct infantry attacks; the tank was now going to break down this deadlock through its ability to cross wire and trenches under fire with far less risk than infantry could ever hope for. Mechanically, the machine was far from perfect, consequently, it was laid down, as a general rule, that never fewer than two tanks should operate together, and when possible not fewer than four.
From a military point of view the penetration of a line of defence does not simply mean passing straight through it, but cutting it in half, and then by moving outwards as well as forwards to push back and envelop the flanks thus created and so widen the base of operation to admit the movement forwards of reserves and supplies, and the movement backwards of casualties and tired troops. A man getting through a hedge first selects a weak spot (point of attack), he then forces his arms through the branches (penetration), and pushing them outwards (envelopment), forms a sufficiently large gap (base of operations) to permit of his body (army) passing easily through the hedge (enemy’s defences).
The operation of penetration with tanks is just the same. Take a half section, two machines; this half section first penetrates the enemy’s defences by crossing them (see diagram 7), then by moving outwards, say to the left, starts enlarging the base by driving the enemy towards A, and so makes a gap between the point of penetration and A, for the infantry to move through. As the enemy may, whilst the tanks are working towards A, seek refuge in his dugouts and “come to life” again after the tanks have passed by, it is necessary that the tanks should be followed by an infantry “mopping up” party which will bomb the dugouts and so render “coming to life” less frequent. As the bombing party has to work up the trench with the tank, it cannot hold the trench once it is cleared, consequently another party of infantry should follow the bombers, whose duty it is to garrison the trench on it being captured. We therefore find that even in the smallest tank attack two parties of infantry are required: in trench warfare these are known as “moppers up” and “support,” and in field warfare as “firing line” and “supports.” Frequently it is as well to add another party, a “reserve,” so that some definite force of men may be held in hand to meet any unexpected event.