Naval artillery, or naval riflery, is artillery mounted on a warship for use in naval warfare. Naval artillery has historically been used to engage either other ships, or targets on land; in the latter role it is currently termed naval gunfire fire support. In the 20th century naval artillery also gained an anti-aircraft role.
The idea of ship-borne artillery dates back to the classical era. Julius Caesar indicates the use of ship-borne catapults against Britons ashore in his Commentarii de Bello Gallico. The dromons of the Byzantine Empire carried catapults and fire-throwers. From the late Middle Ages onwards, warships began to carry cannon of various calibres.
From the 16th century onward, the gun became the most important weapon at sea. Galleys were the first naval vessels to carry artillery powerful enough to sink ships and batter down outdated medieval fortress walls. Around the same time sailing warships began to carry an increasing number of guns, most of them on their broadsides. Initially, tactics of sailing ships were geared towards boarding, but as the number guns steadily increased throughout the 16th and 17th century, tactics changed. By the 1650s, the line of battle had developed as a tactic that could take advantage of the broadside armament. This method became the heart of naval warfare during the age of sail, with navies adopting their strategies and tactics in order to get the most broadside-on fire. This state of affairs continued into Napoleonic Wars, where the British Royal Navy met with success over its French opponents in part because of its ability to deliver faster fire from its cannon, directed into the heart of an enemy ship at close range.
During the 19th century naval artillery increased in size and power. The advances in metallurgy and chemistry meant that it was possible to build heavier guns, each firing an explosive shell rather than solid shot. Ships started to carry a smaller number of heavy, long-ranged guns rather than dozens of cannon. This trend began in the 1840s and accelerated after the invention of the ironclad warship around 1860, with some ironclads carrying extremely heavy, slow-firing guns of calibres up to 16.25 inches. These guns were the only weapons capable of piercing the ever-thicker iron armour on the later ironclads; however given their slow rate of fire and the great difficult of handling them, it is perhaps unlikely that they would ever have scored a hit.
The introduction of the quick-firing gun in the 1890s served to reverse this trend to an extent. The pre-dreadnought battleships of this period relied as much on their quick-firing secondary battery (typically of 6 inches in calibre) as they did on their main armament (typically 12 inches in calibre). However the improved rate of fire and range of the heavy guns meant that battleships switched to an "all-big-gun" armament, beginning with HMS Dreadnought, launched in 1906. Dreadnought set the tone for battleships of the rest of the 20th Century; while the calibre of heavy guns increased (to as far as 18.1 inches in the Japanese Yamato class) the basic principle remained the same. Smaller ships, for instance cruisers and destroyers, made use of smaller-calibre weapons which were also found on battleships as the secondary armament.
After World War II, the guided missile began to replace the naval gun as the principal surface-to-surface weapon, at the same time as the rise of the aircraft carrier meant that the surface combatant itself became less important. After 1945 no new ships were begun using heavy guns, though a small number of battleships and cruisers continued in service. The United States Navy's Iowa class battleships were retained in service until the early 21st century, in large part because of their unparalleled fire support capabilities. Today many destroyers and frigates carry a single gun of 3 inches to 5 inches in calibre which is capable of a mixture of fire-support, anti-surface and anti-air fire missions, but it is not regarded as the principal weapon system. Otherwise, the principal role of naval artillery is for short-ranged anti-air and anti-missile defence, for instance with the popular 20mm Phalanx CIWS system.