A moment's consideration will reveal how far-reaching the differences are. Let us ask ourselves what are the main ideas around which all the military lore turns. It may be taken broadly that the general principles are three in number. Firstly, there is the idea of concentration of force, that is, the idea of overthrowing the enemy's main strength by bringing to bear upon it the utmost accumulation of weight and energy within your means; secondly, there is the idea that strategy is mainly a question of definite lines of communication; and thirdly, there is the idea of concentration of effort, which means keeping a single eye on the force you wish to overthrow without regard to ulterior objects. Now if we examine the conditions which give these principles so firm a footing on land, we shall find that in all three cases they differ at sea, and differ materially. Take the first, which, in spite of all the deductions we have to make from it in the case of limited wars, is the dominating one. The pithy maxim which expresses its essence is that our primary objective is the enemy's main force. In current naval literature the maxim is applied to the sea in some such form as this: "The primary object of our battle-fleet is to seek out and destroy that of the enemy." On the surface nothing could look sounder, but what are the conditions which underlie the one and the other? The practical value of the military maxim is based upon the fact that in land warfare it is always theoretically possible to strike at your enemy's army, that is, if you have the strength and spirit to overcome the obstacles and face the risks. But at sea this is not so. In naval warfare we have a far-reaching fact which is entirely unknown on land. It is simply this--that it is possible for your enemy to remove his fleet from the board altogether. He may withdraw it into a defended port, where it is absolutely out of your reach without the assistance of an army. No amount of naval force, and no amount of offensive spirit, can avail you. The result is that in naval warfare an embarrassing dilemma tends to assert itself. If you are in a superiority that justifies a vigorous offensive and prompts you to seek out your enemy with a view to a decision, the chances are you will find him in a position where you cannot touch him. Your offence is arrested, and you find yourself in what, at least theoretically, is the weakest general position known to war.