Bay of Biscay and on 15 December she encountered and sank the Italian submarine . In the autumn of 1942, Thunderbolt was converted with her sister ships and to carry two "Chariots" (a type of manned torpedo) and their crews for operations against Axis shipping in harbour, and was transferred with them to the Mediterranean Sea in December 1942. Their first mission, Operation Principal, was undertaken in December 1942, the three boats taking their charges to targets around the Mediterranean. Thunderbolts objective was shipping in Cagliari, but the operation was not a success, and P311 was lost at La Maddalena, her intended target. A second operation against Palermo harbour in January 1943 was more successful. On 2–3 January, the manned torpedoes entered the harbour and mined the ships there, sinking the hull of the incomplete light cruiser Ulpio Traiano and the freighter . A further mission to Tripoli harbour took place on 18 January. This was to prevent the Axis using blockships to neutralize Tripoli harbour, which was about to be occupied by the British Eighth Army. On 20 February 1943, Thunderbolt shelled the Albanian sailboat Villanzen Veli off Bari. The British submarine was forced to dive and escape by the combined fire of the Italian auxiliary cruiser Brindisi and a coastal battery, while the sailboat only received light damage. Thunderbolt was sunk on 14 March 1943 off Sicily by the Italian corvette Cicogna, which had detected her and attacked with depth charges. Thunderbolt sank in of water, with the loss of all hands. Appearance in the media The 1950 film Morning Departure, directed by Roy Ward Baker, was based on a stage play of the same name by Kenneth Woollard that itself was based on the loss of HMS Thetis (N25). The play was very popular at the time the film was made. Besides being presented on stage in several theatres in Britain, it had already been made as a live TV play by the BBC, first on 1 December 1946. The film starred John Mills and Richard Attenborough and was the feature film debut of Michael Caine. The actor James Hayter, who was a relative of one of the Naval Officers who died in HMS Thetis, Commander Reginald Hayter RN, plays the cook A/B Higgins in the film. It features the accidental sinking of a British submarine, HMS Trojan, when on exercise. The submarine detonates an unexploded mine