When war calls out the whole manhood of many nations and turns them into fighting forces, it is obvious that there cannot be equality of force in all the theatres. Where either side is weaker, it is compelled locally to adopt the same tactics that a defeated force adopts. It must, that is to say, go upon the defensive. It entrenches and fortifies itself. Thus, as military operations, the attack and defence of fortifications may become general, and this without either side being necessarily able to inflict the pressure of siege upon its opponent, siege being understood to mean severing of communications with the outside world. But, clearly, where siege is possible, as was the case with Metz and Paris, the attacking force becomes also the investing force. It can rely upon the straits to which it can reduce the besieged to bring about that surrender which, _ex hypothesi_, would have been the result of the battle had the weaker not declined it. Battle and siege are thus in essence complementary modes of war and all military action may roughly be defined as fighting, or some method of postponing fighting, or steps or preparations towards fighting. SEA WAR War at sea is carried on, as we have seen, by naval fleets. The immediate object of a fleet is to find, defeat, and destroy the enemy’s fleet. The ultimate or further objective which is gained by such destruction is to monopolize the use of the sea, as the master highway, by retaining freedom for the passage of the victor’s ships while denying such passage to those of the defeated. The power to insist on this exclusive control of sea communications is called “command of the sea.”