When Benito Mussolini declared war on France and Britain on 10 June 1940, he had a secret weapon which he believed would release Britain's hold on Gibraltar, Malta, Corfu, Crete and Alexandria. The British Mediterranean Fleet was a threat to the Italian Empire in Libya, Eritrea, Somalia, Ethiopia, Albania and the plan to occupy Yugoslavia and create Mussolini's 'Mare Nostrum'. Since 1935 Italian naval engineers had developed a torpedo with a detachable warhead of 300 kilograms of explosive, enough to blow a hole in any ship. Two divers, termed 'sea devils' by their commander, wore specially designed protective gear and breathing equipment, and navigated these 'maiali' (pigs) to sink battleships, destroyers, frigates, cruisers as well as oil tankers and merchant shipping. The First Flottiglia MAS (motoscafo armato silurante - torpedo-armed motorboat) was set up in 1939, renamed Decima Flottiglia MAS in 1940. Production of torpedoes and equipment began, swimmers were recruited, special diving schools and training camps were established. 'Regia Marina' submarines were modified to carry the torpedoes and their crews to the target area. Bernard O'Connor's 'Italy's Mediterranean Sea Devils' investigates the successes and failures of the 'Decima Flottiglia MAS' using not just first-hand Italian divers' accounts of their exploits but also reports of the British Defence Security Officers and intelligence officers whose job it was to defend British overseas interests. Briain's counter-intelligence and sabotage sections learned an enormous amount about their enemy's modus operandi from retrieving their discarded equipment and interrogating captured sea devils, allowing sophisticated defences to be introduced. This documentary history also includes contemporary newspaper articles from Britain, Australia and the United States which report some of the attacks but also shed light on the changing wartime conditions in the Mediterranean until the Italian armistice in September 1943.