The Great Siege of Gibraltar was an unsuccessful attempt by Spain and France to capture Gibraltar from the British during the American War of Independence. This was the largest action fought during the war in terms of numbers, particularly the Grand Assault of 18 September 1782. At three years and seven months, it is the longest siege endured by the British Armed Forces.

France and Spain sought to secure Gibraltar, which was a key link in Britain's control of the Mediterranean Sea, and expected its capture to be relatively quick—a precursor to a Franco-Spanish invasion of Great Britain.[22]

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