'Alloy' was a British unrealised early plan for the occupation of the Azores islands group, a Portuguese possession in the Atlantic Ocean, should a threat of a German or, later, Vichy French seizure start to become apparent (17 June/autumn 1940).

The origins of the plans lay with Prime Minister Winston Churchill, who in the period immediately before the fall of France in June 1940 became concerned for the security of the British convoys plying the central and southern parts of the Atlantic in the event that Spain entered the war on the Axis side or Germany received permission from General Francisco Franco y Bahamonde’s Falangist government in Spain to move German forces across Spain to attack Gibraltar in 'Felix'. Either of these eventualities could have been followed by Spanish and/or German moves into other Spanish possessions, or the seizure of the Azores islands group.

These threats seemed to be intensified by the surrender of France and the creation of the semi-collaborationist Vichy French administration in the part of France left unoccupied by the Germans. This government still controlled major naval assets as well as large overseas territories including French North Africa and French West Africa, where there were major ports and naval bases at Bizerte, Oran, Algiers, Casablanca and Dakar. The neutralisation of Gibraltar by Spain and/or Germany would have opened the way for the movement of powerful Vichy French naval forces from the Mediterranean to the west coast of Africa on the Atlantic, and from Casablanca and Dakar amphibious undertakings could then possibly have been launched against the Atlantic island groups.

On 17 June Churchill minuted A. V. Alexander, the First Lord of the Admiralty, to initiate the start of Royal Navy planning for the 'Alloy', 'Bugle' and 'Shrapnel' plans to take the Azores, Canary and Cape Verde islands respectively.

'Alloy' paved the way for 'Brisk'.