A warship is any ship designed primarily with combat in mind, as opposed to merchant ships, transport ships, and recreational ships. They generally have some degree of built in offensive capability, and are also built to sustain more damage than other classes of ships. They may also be designed to be more maneuverable than merchant ships. During times of active war, merchant ships may be armed to function more as warships, in order to supplement a military and to defend themselves in order to safely transport goods. Generally, a warship is a part of a larger national Navy, although in some cases an individual or large business entity may have a warship or group of warships for their own personal ends.
In the distant past, the great fleets of Greece, Persia, and Rome consisted of groups of a galley-type warship. These ships were fairly cumbersome, and relied largely on their own weight as a weapon, ramming other ships. Battles consisted of the ships moving into close quarters, where the crews could attack one another with hand weaponry. An exception to this was for a brief period in the Hellenistic Age, lasting until about the 2nd century BCE, when catapults were used to attack from ship to ship. After they fell out of use, projectile attacks were not seen widely again until roughly the 16th century.
In the 16th century, the warship had evolved significantly. They now were ships of sail, much faster, much more maneuverable, and equipped with cannons that could be quickly reloaded and fired to devastate other ships and to attack fortifications on shore. By the mid-17th century the warship had evolved to truly devastating proportions, with large man-of-wars carrying dozens of cannons, and massive sea battles taking place regularly.
By the 19th century things had changed once again. The warship now became a vehicle powered by steam, and instead of shooting cannons they began using exploding shells. With exploding shells came the need for more advanced shielding, which led to the introduction of metal armor. The warship had become ironclad, and weapons were placed on rotating turrets, allowing a smaller number of guns to target much more precisely without the ship having to be turned broadside to a target.
In 1906 the British Navy released the Dreadnought, a massive steam-powered, heavily armored warship equipped exclusively with large guns for attacking other ships from great distances. This warship was largely impervious to earlier designs, and every other national Navy released its own versions of the modern warship within a few years. At the same time, a faster, more maneuverable, but less armored type of warship was developed, called a battlecruiser.
World War II saw a great deal of development of the warship as well. The submarine, which had really been developed during World War I, came into full prominence with the German U-Boat, which proved to be brutally effective at shutting down shipping lines. The aircraft carrier was also developed during this time, acting as a mobile launching ground for air attacks, allowing enemies to attack decisively and with the element of surprise.
In the modern age, there are seven main groupings of warship: the destroyer, the cruiser, the frigate, the corvette, the submarine, the aircraft carrier, and the amphibious assault ship, as well as the now largely defunct battleship class. Most ships used by Navies today are of the destroyer class, although increasingly these distinctions have become blurred, as ships are loaded down with weaponry meant to assault air, sea, and land. As mines and torpedoes have also become less of an issue, armor has also been reduced significantly on the modern warship, leading to sleeker, less-protected vessels.