'Principal' (iii) was a British attack with 2.5-kt Chariot manned torpedoes on targets in the Italian ports of Palermo and La Maddalena on the islands of Sicily and Sardinia respectively (2/3 January 1943).
By December 1942 the British 10th Submarine Flotilla based on Malta had reached a strength of 12 boats within an Allied total of 22 boats (including one Free Yugoslav and four Free Greek boats) in the Mediterranean. In December these units sank 19 Axis vessels totalling 43,868 tons. In the same month another type of underwater weapon was added to the British armoury in the Mediterranean with the arrival in Malta of the first Chariots, or manned torpedoes, under the command of Commander G. M. S. Sladen.
The Chariots were despatched from Malta on their first offensive operations, against Palermo and La Maddalena, just before the end of 1942.
P311 and its three Chariots (and 10 'charioteers') were lost with all hands en route to La Maddalena, but five other Chariots carried by Trooper (three) and Thunderbolt (two) penetrated into Palermo harbour, where the new light cruiser Ulpio Traiano was sunk and the 8,657-ton passenger/cargo ship Viminale damaged on the night of 2/3 January 1943. All of the Chariots were lost by being scuttled, or as a result of equipment malfunction or human error. One 'charioteer' died in the attack, and Unruffled recovered two others. Five had to land and were taken prisoner. Two of these prisoners later escaped in Rome and hid in the Vatican until Lieutenant General Mark W. Clark’s US 5th Army liberated Rome in June 1944.
The second half of the 'Principal' (iii) operation left two Chariots and eight 'charioteers' on Malta. On 18/19 January 1943 these two remaining Chariots were carried by submarines to attack the ships with which the Germans hoped to block Tripoli harbour, a logistic base which was urgently needed by General Sir Bernard Montgomery’s British 8th Army as it advanced to the west across the northern coast of North Africa after the 2nd Battle of El Alamein. The 'charioteers' arrived too late and a blockship was sunk in the harbour mouth. None of the men or chariots returned to Malta.
On 16 April the British sent 14 new 'charioteers' to Malta, and shortly after them examples of the new 4.5-kt Chariot Mark II with a 1,100-lb (499-kg) Torpex HE warhead. In June the British submarine Unseen carried three chariots from Malta to Sicily, where the 'charioteers' surveyed 100 miles (160 km) of coast, examining beaches for 'Husky' (i). Late in June another six Chariots reached Malta for an operation planned against the Italian fleet anchorage at Taranto, but with the fall of Benito Mussolini and the installation of a government headed by Maresciallo d’Italia Pietro Badoglio the planned attack on Taranto was cancelled and all the 'charioteers' were sent to the main base at Loch Cairnbawm on the north-west coast of Scotland.
On 24 September four Chariots and 12 'charioteers' were despatched from Loch Cairnbawm to Lunna Voe in the Shetland islands group to train in for operations among the Norwegian islands, and on 14 October a British light warship carrying two Chariots and four 'charioteers' sailed from Lunna Voe to Tevik Bay in Norway, but German aircraft found the British vessel and attacked it, causing significant damage but not preventing its return to the UK.
Later in the same year, another British vessel, with two Chariots and four 'charioteers', departed Lunna Voe for the Nordfjord in Norway, but no target for the Chariots was discovered and the vessel returned to the Shetland islands group.
On 11 November another such effort was launched, with two Chariots and four 'charioteers' delivered from Lunna Voe in this instance to Tevik Bay in Norway to attack any ship which entered Askvoll harbour. After two days no German ship had arrived and there was a growing threat that the harbour would be closed by ice, so the British party set off back to the Shetland islands group, jettisoning the two Chariots en route because of adverse weather.
In May 1944 Chariots and 'charioteers' were sent from the UK to Trincomalee in Sri Lanka, and at much the same time Chariots were used for a survey of the sea bed off the Normandy coast of German-occupied France in preparation for 'Overlord'.
On 2 June, after the amalgamation of the British and southern Italian manned torpedo forces in the Mediterranean, the Italian destroyer Grecale sailed from Bastia in Corsica to La Spezia carrying three motor torpedo boats and Italian frogmen including Luigi Durand De La Penne, and also two British Chariots, for an attack on the Italian heavy cruisers Bolzano and Gorizia, which had been seized by the Germans after the Italian armistice of 9 September 1943. Grecale launched the boats, which then carried the Chariots and their 'charioteers' to a release point some 3 miles (4.8 km) off the harbour of La Spezia. One Chariot developed a leak in its buoyancy tank and had to be abandoned, but the other sank Bolzano. This thwarted a German plan to sink the cruisers as blockships in the harbour entrance. The 'charioteers' did not manage to rendezvous with the motor boats, so they came ashore and linked up with Italian partisans. In August one successfully crossed the Arno river to reach the Allies, but the other three were seized by the Germans while trying to do the same.
On 27/28 October the British submarine Trenchant carried two Chariots to an attack on the harbour of Phuket island in Thailand. The submarine launched the Chariots some 6 miles (9.7 km) from the harbour, where the only targets were a pair of commandeered Italian ships, Sumatra and Volpi, each of about 5,000 tons. Six hours later the 'charioteers' returned to their parent vessel with the Chariots (the only time this was achieved), but during the return voyage the submarine received a report of Japanese naval activity in the area and therefore jettisoned the Chariots so it could move more rapidly. Trenchant delivered the four 'charioteers' back to Trincomalee.
This is believed to have been the last combat operation undertaken by manned torpedoes, but after the end of World War II, the British used Chariots to aid in the clearance of mines and wrecks in harbours.