The navies are resp onsible for the air defence (AD) of their ships at sea while there are varying arrangements for their shore establishments which differ from country to country. The earliest deployment of naval personnel in AD was during World War I when in 1914 Royal Naval Volunteer Reserve (RNVR) was employed in Britain to man AD guns and search lights for the defence of ports against German air raids. Those days, AD was called anti-aircraft (AA). The German air raids increased in 1915 but the then AD guns like the 75mm and 3-inch were not effective. Thus a naval gunnery expert was appointed to make improvements in the guns as well as air defence arrangements, especially of London. The naval 3-inch gun was then adopted for the AD of Britain. This gun was also inducted into the Army. As most of the air attacks were during night, other methods like illumination of the target with search light and acoustic methods for detection were also developed. QF 3inch 20cwt (76) gun with a new field mounting was introduced in 1916.

With the development of air power, ships at sea also became lucrative targets from the air, thus, various types of cannons and guns were placed on board for AD. Smaller boats and ships have machine-guns or fast cannons, which can be very effective when connected with a radar-fire-control system. The Japanese attack on Pearl Harbour brought the use of air attack against ships into the centre stage where a mass air attack was carried out by the Imperial Japanese Navy against the US naval base at Pearl Harbour, Hawaii, on December 7, 1941. It was aimed to prevent the US fleet from interfering with the Japanese operations in the region and took the US Navy by complete surprise. The US Naval Fleet at Pearl Harbour was attacked by 353 Japanese fighters, bombers and torpedo planes which were launched from six aircraft carriers. The air raid was carried out in two waves and was able to sink four US battle ships and damage eight. They also managed to sink/damage three cruisers, three destroyers, an anti-aircraft training ship, one minelayer and destroy 188 US aircraft. At least 2,402 US personnel were killed and 1,282 wounded. There was also massive damage to the shore establishments of the base. The attack came as a shock to the US, leading it to join World War II and declare war on Japan. Since then there has been no looking back at the use of air power against the Navy at sea. Many type of sensors and weapons have been designed especially for use against naval ships and submarines.

Air Defence Guns

There has been a continuous evolution in the development of AD gun systems. The gunnery solution for moving targets is complex, and for aerial targets, it becomes even more difficult as the target can simultaneously move in three dimensions at supersonic speed. Adaptations of the standard autocannon, originally intended for air-to-ground use and heavier artillery systems were commonly used for most anti-aircraft gunnery, starting with standard pieces on new mountings and evolving to specially designed guns with much higher performance prior to World War II. Initially, the British had the 3-inch gun and the US Navy came up with the 1.1'/75 (28mm) gun to replace the inadequate .50 calibre. Smaller AD guns were more popular due to their low cost and ease of following the aerial target as compared to the heavier guns which were used for their longer range. Some examples of these guns were the 40mm auto-cannon and the 8.8 cm FlaK 18, 36 gun, both designed by Bofors of Sweden. The British Army eventually adopted the QF 3.7 inch AA gun as the most commonly used type. Britain also had QF 4.7 inch Mk VIII naval gun, QF 4 inch Mk V,QF 5.25 inch Mark I naval gun and QF 4 inch Mk XVI naval guns during World War II. Mk XVI version spilled into the cold war era. The Japanese used 8 cm/40 3rd Year Type naval AA gun on many Japanese ships built between 1910 and 1930. 10cm/65 Type 98 AA gun was used on their 1942 Akizuki class destroyer, aircraft carrier Taihõ and Japanese cruiser Õyodo. The 40mm Bofors AA gun became extremely popular with the navy as well as the army and was deployed in large numbers.

There were many other refinements in the guns and ammunition. The sighting system was improved, hydraulics was added to the traverse and elevation gears so that the aerial target becomes more effective. Various types of fuse systems like barometric, time delay and proximity were tried out. The aim of all this was to improve the cumulative kill probability of the system. The control of guns with the help of fire-control radar was the ultimate refinement which is still current today but with improvements in the performance parameters of guns and fire control radars. The 57mm dual purpose naval gun was developed in 1964 by Bofors Defence (which has been a part of BAE Systems AB since March 2005) and produced in 1966 as 57mm Mark 1. It was initially deployed on smaller coastal patrol craft and fast attack craft. The gun has been upgraded and improved many a times. During 2004, BAE Systems AB developed Mk 110 57mm gun and offered it to the US Coast Guard and the US Navy in 2006, since it has been deployed on littoral combat ships of the US Navy like USS Independence and USS Freedom.

Phalanx Close in Weapon System (CIWS): This system was designed and manufactured by the General Dynamics Corporation, Pomona Division (now a part of Raytheon). Phalanx was developed as a close in weapon system which would provide terminal defence or point defence against anti-ship missiles including high-g and manoeuvring sea-skimmers. It is radar controlled and has 20mm calibre 6 barrel Gatling gun. Phalanx CIWS is a universally accepted system which is deployed on every class of surface combat ship by the US Navy. The US Coast Guard has deployed it on Hamilton class and Legend class cutter. It is also deployed with navies of 23 nations. The US Navy began deploying it on selected non-combatant vessels in 1984. The CIWS can be used effectively against any low flying object in the terminal stage.

Rail Gun: The gun systems have almost reached a plateau with respect to range, rate of fire and ammunition. A highly futuristic system is being developed in the US called the rail gun which is an electrically powered electromagnetic projectile launcher based on similar principles to the homopolar motor which is an electric motor that works without the commutator. During February 2008, the US Navy tested a rail gun which fired a shell at a muzzle velocity (MV) of 5,600 miles (8,960 km) per hour using 10 megajoules of energy. The MV is expected to exceed 13,000 miles (20,800 km) per hour. It is planned to be accurate enough to hit a five meter target from 200 nautical miles (370 km), firing at the rate of firing of ten shots per minute. It is expected to create damage equal to a Tomahawk at a fraction of the cost. At present the rail gun is being developed for static targets but future systems can be developed for AD role as well.

Missile Systems

Missiles are employed in the Navy either on board ship as surface-to-air missiles (SAMs) or on maritime aircraft for air-to-air combat in order to provide fleet AD. Some examples of both types are given below.

Italy

Aspide: Aspide is an Italian mediumrange air-to-air and surface-to-air missile which had a semi-active radar-homing seeker. It was very similar to the American AIM-7 Sparrow. It was employed on F104 Starfighter and later on replaced by MBDA’s Aster. China acquired Aspide Mk 1 and later on developed its own version called LY-60.

Israel

Barak 1: Barak is a shipborne Israeli SAM system which provides point AD against aircraft, anti-ship missiles, and UAVs. It is meant to replace or complement gun-based CIWS platforms, such as the Phalanx CIWS. The missiles are mounted in an eight cell container and are launched vertically. The radar system provides 360 degree coverage and can engage an incoming missile as close as 500 metres away from the ship. Its operational range is 10-12 km and flight altitude is from 500 m-5.5 km. It is in service with the Indian Navy. Its successor called Barak II and Barak 8 is also under development which will have longer range. It is manufactured by IAI and Rafael Advanced Defense Systems Ltd.

United States

AIM-7 Sparrow: AIM-7 Sparrow is an US, medium-range semi-active radar homing air-to-air missile used by the US Air Force, Navy and Marine Corps. It is also used by other countries. Sparrow and its versions were the US’ and its ally’s beyond visual range (BVR) air-to-air missile from the late 1950s until the 1990s. It is still in service and is being phased out by AIM-120 advanced medium-range air-to-air missile (AMRAAM). The range can vary from 32 to 50 km depending on the version. It is manufactured by Raytheon.

RIM-162 Evolved Sea Sparrow Missile (ESSM): ESSM has been developed from RIM-7 Sea Sparrow missile which was employed to protect ships from attacking missiles and aircraft. ESSM is designed to counter supersonic manoeuvring anti-ship missiles, it is larger than Sea Sparrow, has a more powerful rocket motor for increased range and agility and has a range of 50 km. It is manufactured by Raytheon.

RIM-66 Standard MR (SM-1MR/SM-2MR): RIM-66 is a medium-range SAM developed for the US Navy to replace RIM-2 Terrier and RIM-24 Tartar deployed on many US ships since the 1950s. The RIM-67 Standard (SM-1ER/SM-2ER) is an extended range version with an operational range from 74 to 170 km. Vertical launch has been used in the US Navy since 2003 and the latest version is deployed on ships like Ticonderoga class cruisers and Arleigh Burke class destroyers. Raytheon is the main manufacturer of this system.

RIM-161 Standard Missile 3 (SM-3): This is a ship-based missile system used by the US Navy to intercept short- to intermediaterange ballistic missiles as a part of Aegis Ballistic Missile Defense System with a range of more than 500 km. It has also been employed in an anti-satellite role against a satellite at the lower end of the low earth orbit. It is deployed with the US Navy and the Japan Maritime Self-Defense Force. It is manufactured by Raytheon and Aerojet.

RIM-174 Standard Extended Range Active Missile (ERAM): It is also called Standard Missile 6 (SM-6) and is the latest system. It is designed for extended range anti-air warfare (ER-AAW) role against fixed and rotary-wing aircraft, UAVs and antiship cruise missiles in flight, both over sea and land. It has an operational range of 240 km and is manufactured by Raytheon.

AIM-120 Advanced Medium-Range Airto-Air Missile (AMRAAM): AMRAAM is a state-of-the-art air-to-air BVR which has active guidance and is a fire-and-forget missile system. AMRAAM is successor to AIM-7 Sparrow missile series. The new missile is faster, smaller, lighter, and has improved capabilities against low flying targets. It has a data link to guide the missile to a point where its active radar switches on for providing terminal guidance. Its operational range varies from 55 to more than 180 km. AMRAAM is required to be integrated on smaller aircraft like Sea Harrier. The US Navy plans to integrate them with F/A-1C8 Hornet and F/A-18E/F Super Hornet.