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The GIUK gap is an area in the northern Atlantic Ocean that forms a naval warfare choke point. Its name is an acronym for Greenland, Iceland, and the United Kingdom, the gap being the open ocean between these three landmasses. The term is typically used in relation to military topics.
The GIUK gap was particularly important to the British Royal Navy, as any attempt by northern European forces to break into the open Atlantic would have to do so either through the heavily defended English Channel, one of the world's busiest seaways, or through one of the exits on either side of Iceland. When also considering British control over the strategic fortress of Gibraltar at the entrance to the Mediterranean, Ireland, Spain, France, and Portugal are the only Continental European countries that possess direct access to the Atlantic Ocean that cannot easily be blocked at a choke point by the Royal Navy.
In the modern period, the exploitation of the GIUK gap by northern forces and measures to patrol and secure the gap by opposing forces has played an important role in naval and overall military planning.
World War II 
During World War II the gap was used by German ships to break out from their bases in northern Germany and Norway in an attempt to attack convoys, but these actions were generally unsuccessful due to blocking efforts in the North Sea and the GIUK gap. The Germans were aided tremendously with the fall of France, when they were able to base their submarines on the French coast. Between 1940 and 1942 the Denmark Strait between Iceland and Greenland was one of the few areas that RAF patrol bombers could not reach, and thus became the centre for considerable action.
The origin of the term "gap" can be traced to this period, when there was a gap in air coverage known as the Mid-Atlantic gap or "Greenland air gap". This gap was an area that landbased aircraft could not reach and as a result were not able to carry out their anti-submarine duties. The gap was eventually closed in 1943 with longer-ranged versions of aircraft such as the Short Sunderland and B-24 Liberator, making submarine actions in the Atlantic nearly impossible.
Cold War 
The gap again became the focus of naval planning in the 1950s, as it would be the only available outlet into the ocean for Soviet submarines operating from their bases on the Kola Peninsula. The primary concern was that if the Cold War "turned hot", naval convoys reinforcing Europe from the U.S. would suffer unacceptable losses if Soviet submarines were allowed to operate in the North Atlantic. The United States and Britain based much of their post-war naval strategy on blocking the gap, eventually installing a chain of underwater listening posts right across it, known as SOSUS.
The Royal Navy's primary mission during the Cold War, excluding the nuclear deterrent role, was that of anti-submarine warfare (ASW). The development of the Invincible-class anti-submarine carriers was part of this doctrine with their primary mission being anti-submarine warfare using the Sea King helicopter. The Type 23 frigate was to be a pure ASW platform; its mission expanded following the Falklands War.
Likewise, the Soviets planned to use the gap to intercept any NATO ships, especially aircraft carriers, heading towards the Soviet Union. Ships and submarines as well as Tupolev Tu-142 maritime surveillance aircraft were to be used to track the threatening ships.
In popular culture 
- The GIUK line is mentioned in the film The Bedford Incident. It is also in a few books such as Tom Clancy's Red Storm Rising and The Hunt for Red October. In Red Storm Rising, the Soviet Union launches a surprise attack on the NATO airbase NAS Keflavik.
- Early editions of the Harpoon naval warfare simulation were based around defending the GIUK Gap. Tom Clancy used the simulation to test the naval battles for Red Storm Rising.
- The location of Iceland in the gap made it a participant in the cold war and a target for a nuclear strike, especially through the introduction of the aforementioned atomic bomber NATO base. Halldor Laxness dramatized the tension of these geopolitics from the perspective of an Icelandic maid in the novel The Atom Station.
See also 
- Battle of the Denmark Strait
- Broad Fourteens
- Communication with submarines
- Long Forties
- Mid-Atlantic gap
- Western Approaches
- "The Dover Strait". Maritime and Coastguard Agency. 2007. Retrieved 2010-04-17.
- "Harpoon Naval Warfare Simulation Game - AGSI - Harpoon Commanders Edition (HCE)".