On the other hand, it is necessary that the sight of the latter must never be interrupted by a friendly ship.

Only one formation allows the ships of the same fleet to satisfy fully these conditions.

That formation is the line ahead [column].

This line, therefore, is imposed as the only order of battle, and consequently as the basis of all fleet tactics.

In order that this order of battle, this long thin line of guns, may not be injured or broken at some point weaker than the rest, there is at the same time felt the necessity of putting in it only ships which, if not of equal force, have at least equally strong sides.