the chief instrument by which a nation extends its military power onto the seas. Warships protect the movement over water of military forces to coastal areas where they may be landed and used against enemy forces; warships protect merchant shipping against enemy attack; they prevent the enemy from using the sea to transport military forces; and they attack the enemy's merchant shipping. Naval ships are also used in blockade-i.e., in attempts to prevent an enemy from importing by sea the commodities necessary for prosecution of the war. In order to accomplish these objectives, naval ships have been designed from earliest times to be faster and sturdier than merchant ships and to be capable of carrying offensive weapons