Naval artillery

Naval artillery is artillery mounted on a warship, originally used only for naval warfare, later also for naval gunfire fire support against targets on land, and for anti-aircraft use. The term generally refers to tube-launched projectile-firing weapons and excludes self-propelled projectiles like torpedoes and rockets, and those simply dropped overboard like depth charges and naval mines.

Origins
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. Although some 16th century galleys mounted broadside cannon, they did so at the expense of rowing positions which sacrificed speed and mobility. Most galleys retained a naval ram as their most effective means of sinking another ship. Most early cannon were placed in the forecastle and aftercastle of a ship where they might be conveniently pointed in any direction. Early naval artillery was an antipersonnel weapon to deter boarders, because cannon powerful enough to damage ships were heavy enough to destabilize any ship mounting them in an elevated castle.

Age of Sail
From the 16th century, the cannon became the most important weapon at sea. Around the same time sailing warships began to carry an increasing number of cannon, most of them firing to the side. As the number of cannon steadily increased throughout the 16th and 17th century, tactics shifted and were no longer geared entirely to boarding. Transition era ships, such as English king Henry VIII's Mary Rose, carried a mixture of cannon of different types and sizes, many designed for land use, and using incompatible ammunition at different ranges and rates of fire. A perier might throw a stone projectile 4000 ft, while cannon could throw a 32-pound iron cannonball 1 mi, and a culverin might throw a 17-pound cannonball 2 km. Swivel guns and smaller cannon were often loaded with grapeshot for antipersonnel use at closer ranges, while the larger cannon might be loaded with a single heavy cannonball to cause structural damage.

In the reign of Queen Elizabeth advances in manufacturing technology allowed the English Navy Royal to start using matched cannon firing standard ammunition, allowing firing of coordinated broadsides. While the cannonball remained the standard projectile for structural damage, other types of ammunition were used for special purposes. The cannonball might be heated on a bed of coals until it glowed cherry-red before loading so it might set fire to sails, rope, wooden splinters or stored gunpowder on the target ship. Cannon might be loaded with chain-shot or bar shot to increase damage to sails and rigging. Cannon might be double-shotted by loading two cannonballs to increase damage at close range.

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. Cannon were mounted on multiple decks to maximize broadside effectiveness. Numbers and caliber differed somewhat with preferred tactics. France and Spain attempted to immobilize ships by destroying rigging with long-range, accurate fire from their swifter and more maneuverable ships, while England and the Dutch Republic favored rapid fire at close range to shatter a ship's hull and disable its crew. British crews trained to fire a broadside every two or three minutes, while French and Spanish crews typically took twice as long to fire an aimed broadside. An 18th-century ship of the line typically mounted 32-pounder or 36-pounder long guns on a lower deck, and 18- or 24-pounders on an upper deck, with some 12-pounders on the forecastle and quarterdeck. By the late 18th century, British and American warships began using carronades to maximize damage at close range.

Industrial Revolution
The Industrial Revolution introduced steam-powered ironclad warships seemingly impervious to cast cannon. The inadequacy of naval artillery caused the naval ram to reappear as a means of sinking armored warships. The rapidity of innovation through the last half of the 19th century caused some ships to be obsolete before they were launched. Maximum projectile velocity obtainable with gunpowder in cast cannon was approximately 480 m/s. Increased projectile weight through increased caliber was the only method of improving armor penetration with this velocity limitation. Some ironclads carried extremely heavy, slow-firing guns of calibres up to 16.25 in. These guns were the only weapons capable of piercing the ever-thicker iron armour on the later ironclads, but required steam powered machinery to assist loading cannonballs too heavy for men to lift. USS Monitor demonstrated the possibilities of a gun turret in 1862.

Breech-loading artillery
Large caliber breech-loading naval artillery became practical with French development of the interrupted screw obturator by Charles Ragon de Bange in 1872. Built-up guns with rifling made cast cannon obsolete by 1880. Breech loading artillery overcame barrel length limitations of cast cannon imposed by the necessity of retracting the cannon into the hull for reloading through the muzzle. Simultaneous availability of longer barrels and slower burning brown powder increased projectile velocities to 650 m/s. Spin-stabilized elongated projectiles offered both reliable positioning of percussion fuzes and improved armor penetration through increased sectional density.

Quick-firing artillery
Underwater hull damage possible with torpedoes encouraged development of small, inexpensive torpedo boats capable of sinking the largest warships. By the end of the 19th century, all warships required a defensive battery of quick-firing guns capable of hitting fast, maneuverable torpedo boats. Most late 19th century warships mounted naval artillery of more than one caliber because of uncertainty about the relative destruction possible from a few large shells (which might miss) in comparison to the increased hit probability of a larger number of less damaging small caliber shells fired within the same time period. Quick-firing guns were initially breech loading weapons firing ammunition small enough to be loaded by hand. Later substitution of brass cartridges for silk powder bags allowed increased rates of fire using sliding wedge breech blocks. Increasing mechanization ultimately enabled similar rates of fire from naval artillery calibers up to 8 in.

Explosive shells
The incendiary properties of exploding shells demonstrated the obsolescence of wooden warships in the 1853 Battle of Sinop; but detonation effectiveness was limited by use of gunpowder bursting charges. Early high explosives used in torpedo warheads would detonate during the acceleration of firing from a gun. After brief use of dynamite guns aboard USS Vesuvius (1888), picric acid became widely used in conventional naval artillery shells during the 1890s. Increased armor penetration became possible when projectile velocities of 800 m/s were obtained as smokeless powder propellants replaced gunpowder about 1900.

Fire Control
Naval artillery was originally aimed by individual gun crews who adjusted their point of aim based on observation of shell splashes with respect to target location. Directors were later placed high in the ship for improved observation to transmit aiming instructions to gun turrets. Pre-dreadnought battleships typically carried two turrets of large caliber guns, and several intermediate caliber guns. These ships confused the fire control directors because of difficulty distinguishing between the shell splashes of the two calibers and applying the required correction to the appropriate guns. This difficulty was resolved by building ships mounting naval artillery of a single caliber.

Explanation of the term Caliber in relation to Naval Rifles
Naval rifles, although constructed and manufactured in roughly the same manners as land based artillery, were built to much more stringent and studious standards than land based weapons, and for good reason. At sea, a weapon had to perform, without fail. There was no ready replacement, nor one that could be readily supplied. Additionally, naval artillery reached sizes and weights virtually unheard of (with a few very rare exceptions) in land based weapons. Over time, the terms of pound (weight of shell) and bore (the actual bore of the weapon) became confused and blurred. Eventually, when the technology existed, the bore (in inches or millimetres) came to be the standard measure. For naval rifles, the initial change was to actual bore, thus facilitating the manufacture of standard projectiles. Concurrently the practice of presenting the measure of the effective length (and therefore range) of the weapon in calibers began to emerge. These were (and are) a measure of the standardized bore of the barrel versus the rifled bore of the barrel. In other words, a 12/45 is 12"X45= the length of the rifled bore of that gun in inches. This explains the differences in both peneration and long range performance of various naval rifles over the years, as a gun of 12/35 versus a 12/50 in most instances will, when presented without range or penetration data, appear to be nearly the same weapon. In addition to the possible improvements in overall performance (i.e. muzzle velocity and striking force), the increase in barrel length also allowed, in some circumstances, an increase in projectile size as well. For example, the American 14/45, as introduced in the New York-class ships, fired a 1250lb. projectile. Later improvements to the design, lengthening the rifle itself and also altering the breech, allowed a 1400lb. projectile and, overall, a greater barrel life. Again we see this pattern with the US 16" guns. The initial design was 45 calibers in length and fired a 2200lb. shell. The later re-design to 50 calibre not only allowed a higher velocity but also a heavier 2700lb. shell, which ultimately came to be accepted as the greatest naval shell ever deployed in combat.

Dreadnoughts
Battleships switched to an "all-big-gun" armament, beginning with HMS Dreadnought, launched in 1906. In comparison to the rapid obsolescence of the preceding half-century, naval artillery changed comparatively little through World War I and World War II. Battleships remained similar to Dreadnought, torpedo boats evolved into destroyers, and ships of intermediate size were called cruisers. All ship types became larger as the calibre of heavy guns increased (to a maximum of 46 cm in the Yamato-class battleships), but the number of guns carried remained similar. Smaller ships used smaller-calibre weapons which were also used on battleships as the defensive secondary armament.

High-angle artillery
Although naval artillery had been designed to perform within the classical broadside tactics of the age of sail, World War I demonstrated need for naval artillery mounts capable of greater elevation. High-velocity naval artillery intended to puncture side armor at close range was theoretically capable of hitting targets miles away with the aid of fire control directors; but the maximum elevation of guns mounted within restrictive armored casemates prevented reaching those ranges. High-angle anti-aircraft guns became necessary as aircraft demonstrated anti-ship capability. Dual purpose guns were devised to protect ships against both torpedo boats and aircraft. Most naval artillery on ships built after World War I was capable of elevating to at least 45° ; and some guns as large as 8 in were capable of elevating to 70° for potential use against aircraft. As the role of destroyers expanded to include protection from submarines, they were fitted with high-angle depth charge mortars (called Y-guns, K-guns or squid).

Support for amphibious landings
Amphibious landings in the Pacific in World War II required an intense pre-landing barrage from heavy guns. However naval gunnery had always focused on opposing fleets. The necessary new tactics were developed at the U.S. Naval gunnery school at Kahoolawee in Hawaii, and perfected in the landings in the Marshalls and the Marianas in 1943. This became the main mission of the American battleships in the war.

Electronic age
Guided missiles began to replace naval artillery as more effective weapons against aircraft and ships in the mid-20th century. Naval artillery calibers greater than 5 in were used primarily for naval gunfire support after 1944; and no new ships were built with larger naval artillery. Submarines shed deck guns as a handicap in modern naval tactics. Destroyers and frigates carry a single gun of 3- to 5-inch calibre (76.2-127mm) as a backup to missile systems and capable of land fire support. Remaining roles of naval artillery like the 20mm Phalanx CIWS system are for short-range defence against targets which cannot be engaged by guided weapons systems. The US 5"/54 caliber Mark 45 gun is capable of firing 20 rounds per minute to a range of 20 miles.

In the early 21st century the use of railguns mounted on ships is under study.