The idea held by many people that the defense of a country can be effected by simply preventing the invasion of its coasts, is a little like the notion of uneducated people that a disease can be cured by suppressing its symptoms. For even a successful defense of a coast against invasion by a hostile force cannot remove the inimical influence to a country's commerce and welfare which that hostile force exerts, any more than palliatives can cure dyspepsia. Every intelligent physician knows that the only way to cure a disease is to remove its cause; and every intelligent military or naval man knows that history teaches that the only way in which a country can defend itself successfully against an enemy is to defeat the armed force of that enemy--be it a force of soldiers on the land, or a force of war-ships on the sea. In naval parlance, "our objective is the enemy's fleet." If the duty of a navy be merely to prevent the actual invasion of its country's coasts, a great mistake has been made by Great Britain, France, and other countries in spending so much money on their navies, and in giving so much attention to the education and training of their officers and enlisted men. To prevent actual invasion would be comparatively an easy task, one that could be performed by rows of forts along the coast, supplemented by mines and submarines. If that is the only kind of defense required, navies are hardly needed. The army in each country could man the forts and operate the mines, and a special corps of the army could even operate the submarines, which (if their only office is to prevent actual invasion) need hardly leave the "three-mile limit" that skirts the coasts. If the people of any country do not care to have dealings outside; if the nation is willing to be in the position of a man who is safe so long as he stays in the house, but is afraid to go outdoors, the problem of national defense is easy. But if the people desire to prevent interference with what our Constitution calls "the general welfare," the problem becomes exceedingly complex and exceedingly grave--more complex and grave than any other problem that they have. If they desire that their ships shall be free to sail the seas, and their citizens to carry on business and to travel in other lands; and if they desire that their merchants shall be able to export their wares and their farmers their grain, also that the people shall be able to import the things they wish from foreign countries, then they must be able to exert actual physical force on the ocean at any point where vessels carrying their exports and imports may be threatened. Naval ships are the only means for doing this. The possibility that an armed force sent to a given point at sea might have to fight an enemy force, brought about first the sending of more than one vessel, and later--as the mechanic arts progressed--the increasing of the size of individual vessels, and later still the development of novel types.