Patrol bomber

A maritime patrol aircraft (MPA), also known as a patrol aircraft, maritime reconnaissance aircraft, or by the older American term patrol bomber, is a fixed-wing aircraft designed to operate for long durations over water in maritime patrol roles — in particular anti-submarine warfare (ASW), anti-ship warfare (AShW), and search and rescue (SAR).

Among other maritime surveillance resources, such as satellites, ships, unmanned aerial vehicles (UAVs) and helicopters, the MPA is an important asset. To perform ASW operations, MPAs typically carry air-deployable sonar buoys as well as torpedoes and are usually capable of extended flight at low altitudes.

History

First World War

The first aircraft that would now be identified as maritime patrol aircraft were flown by the Royal Naval Air Service and the French Aéronautique Maritime during the First World War, primarily on anti-submarine patrols. France, Italy and Austria-Hungary used large numbers of smaller patrol aircraft for the Mediterranean, Adriatic and other coastal areas while the Germans and British fought over the North Sea. At first, blimps and zeppelins were the only aircraft capable of staying aloft for the longer ten hour patrols whilst carrying a useful payload while shorter-range patrols were mounted with landplanes such as the Sopwith 1½ Strutter.Jarrett 2009, p. 59. A number of specialized patrol balloons were built, particularly by the British, including the SS class airship of which 158 were built including subtypes.SS class airship.
Airship Heritage Trust. Retrieved on 18 March 2009.
Charles Vivian, E., ''A History of Aeronautics'' pt.3, ch.V. Retrieved on 28 March 2009.

As the conflict continued, numerous aircraft were developed specifically for the role, including small flying boats such as the FBA Type C, as well as large floatplanes such as the Short 184, or flying boats such as the Felixstowe F.3.Thetford 1978, p. 198. Developments of the Felixstowe served with the Royal Air Force until the mid 20s, and with the US Navy as the Curtiss F5L and Naval Aircraft Factory PN whose developments saw service until 1938. During the war, Dornier did considerable pioneering work in all aluminium aircraft structures while working for Luftschiffbau Zeppelin and built four large patrol flying boats, the last of which, the Zeppelin-Lindau Rs.IV, influenced development elsewhere resulting in the replacement of wooden hulls with metal ones, such as on the Short Singapore. The success of long range patrol aircraft led to the development of fighters specifically designed to intercept them, such as the Hansa-Brandenburg W.29.

Second World War

Many of the Second World War patrol airplanes were converted from either bombers or airliners, such as the Lockheed Hudson which started out as the Lockheed Model 14 Super Electra, as well as older biplane designs such as the Supermarine Stranraer, which had begun to be replaced by monoplanes just before the outbreak of war. The British in particular used obsolete bombers to supplement purpose-built aircraft for maritime patrol, such as the Vickers Wellington and Armstrong-Whitworth Whitley,Andrews 1967, p. 14.Moyes 1967, p. 13. while the US relegated the Douglas B-18 Bolo to the same role until better aircraft became available. Blimps were widely used by the United States Navy, especially in the warmer and calmer latitudes of the Caribbean Sea, the Bahamas, Bermuda, the Gulf of Mexico, Puerto Rico, Trinidad, and later the Azores.

A number of special-purpose aircraft were also used in the conflict, including the American-made twin-engine Consolidated PBY Catalina flying boats, and the large, four-engine British Short Sunderland flying boats of the Allies.Norris 1967, pp. 7, 10–11. In the Pacific theatre, the Catalina was gradually superseded by the longer-ranged Martin PBM Mariner flying boat.Dorr 1987, p. 116. For the Axis Powers, there were the long-range Japanese Kawanishi H6K and Kawanishi H8K flying boats, and the German Blohm & Voss BV 138 diesel-engined trimotor flying boat, as well as the converted Focke-Wulf Fw 200 Condor airliner landplane.Seifert, Karl-Dieter. "Der Deutsche Luftverkehr 1926 - 1945." Bernard & Graefe Verlag, Bonn, 1996. . (in German) pp. 303-304."Concise Guide to Axis Aircraft of World War II." Compiler: David Mondey, Temple Press Aerospace. 1984. . pp. 73-74.

To finally close the Mid-Atlantic gap, or "Black Gap", a space in which Axis submarines could prey of Allied shipping historically out of reach of MPAs, the British Royal Air Force, the Royal Canadian Air Force, and the US Army Air Forces introduced the American Consolidated B-24 Liberator bomber, which had a very long range for the era. The B-24 was also used at the basis for the PB4Y-2 Privateer, a dedicated MPA variant adopted in large numbers by the US Navy, which saw service late on in the Pacific theatre.

During the conflict, there were several developments in Air-to-Surface Vessel radar and sonobuoys, which enhanced the ability of aircraft to find and destroy submarines, especially at night and in poor weather.Anonymous, "Ocean's Depth Measured By Radio Robot," ''Popular Mechanics'', December 1938, pp. 828-830.
/ref> Another area of advancement was the adoption of increasingly effective camouflage schemes, which led to the widespread adoption of white paint schemes in the Atlantic to reduce the warning available to surfaced U-boats, while US Navy aircraft transitioned from an upper light blue-gray and lower white to an all-over dark blue due to the increasing threat of Japanese forces at night-time.

Cold War era

In the decades following the Second World War, the MPA missions were partially taken over by aircraft derived from civilian airliners. These had range and performance factors better than most of the wartime bombers. The latest jet-powered bombers of the 1950s did not have the endurance needed for long, overwater patrolling, and they did not have the low loitering speeds necessary for antisubmarine operations. The main threat to NATO maritime supremacy throughout the 1960s, 1970s, and the 1980s was Soviet Navy and Warsaw Pact submarines. These were countered by the NATO fleets, the NATO patrol planes mentioned above, and by sophisticated underwater listening systems. These span the so-called "GIUK Gap" of the North Atlantic that extends from Greenland to Iceland, to the Faroe Islands, to Scotland in the United Kingdom. Air bases for NATO patrol planes have also been located in these areas: U.S. Navy and Canadian aircraft based in Greenland, Iceland, and Newfoundland; British aircraft based in Scotland and Northern Ireland; and Norwegian, Dutch, and German aircraft based in their home countries.

During the late 1940s, the RAF introduced the Avro Shackleton a specialised MPA derivative of the Avro Lancaster bomber in anticipation of a rapid expansion of the Soviet Navy's submarine force.Jones 2002, p. 43.
An improved model of the Shackleton, the ''MR 3'', was introduced, featuring various structural improvements, along with homing torpedoes and Mk 101 Lulu nuclear depth bombs.''World Aircraft Information Files'' 1997. During the late 1960s, a jet-powered replacement in the form of the Hawker Siddeley Nimrod, a derivation of the De Havilland Comet airliner, begun to be introduced. During the 2000s, an improved model, the BAE Systems Nimrod MRA4, was in development, but was cancelled and eventually substituted for by the Boeing P-8 Poseidon.

The U.S. Navy flew a mixture of MPAs, including the land-based Lockheed P2V Neptune (P2V) and the carrier-based Grumman S-2 Tracker. During the 1970s, the P2V was entirely replaced by the Lockheed P-3 Orion