'C' (i) was a Spanish unrealised plan for the military seizure of Gibraltar from the British (1939).

The northern element of the 'Pillars of Hercules' controlling the eastward entrance to the Mediterranean Sea and this sea’s westward exit to the Atlantic Ocean, Gibraltar had been captured from the Spanish in 1704, during the War of the Spanish Succession, by a combined British and Dutch fleet, representing the Grand Alliance. The seizure was effected on behalf of the Archduke Charles of Austria in his campaign to become king of Spain, and most of the population later left the town, though many settled nearby. As the Alliance’s campaign faltered, the 1713 Treaty of Utrecht was negotiated, which ceded control of Gibraltar to the UK to secure the latter’s withdrawal from the war. Unsuccessful attempts by Spanish monarchs to regain Gibraltar were made with the siege of 1727 and again with the Great Siege of Gibraltar (1779 to 1783) during the American War of Independence. The British possession of Gibraltar has been disputed by Spain ever since that time.