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The GIUK gap

The GIUK gap is an area in the northern Atlantic Ocean that forms a naval warfare chokepoint. 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 is particularly important to the Royal Navy, as any attempt by northern European forces to break into the open Atlantic would have to do so either through the easily defended English Channel 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, Spain (northern coast), France (Atlantic coast) and Portugal are the only mainland European nations that have direct access to the Atlantic ocean in a way that cannot be easily blocked at a choke point by the Royal Navy.

In the modern period, the explotation 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 planing.

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 couldn't reach, and thus became the center 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 "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.

The gap again became the center 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 that was 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 British 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 Tu-95 Bear maritime surveillance aircraft to keep tabs on the threatening ships.

The GIUK line is mentioned in a few books as a significant plot element, such as Tom Clancy's Red Storm Rising and The Hunt for Red October.

The GIUK gap is also a route for migratory birds such as the northern wheatear to cross the Atlantic to reach Greenland and Eastern Canada.

• Western Approaches
• Broad Fourteens
• Long Forties
• Battle of the Denmark Strait