HMS Regent was a Rainbow-class submarine designed and built by Vickers Shipbuilding and Engineering in Barrow-in-Furness for the Royal Navy, and was launched on 11 June 1930.

There Medway, the Royal Navy's first purpose-built submarine depot ship, supported her and her classmates, Rainbow, Regulus, and Rover.

[3] Citta di Messina, of 2,742 tons, was under escort by the Italian torpedo boat Centauro, which was able to rescue 166 survivors.

[2] On 21 February, Regent attacked three merchant vessels at 33°41′N 12°48′E / 33.683°N 12.800°E / 33.683; 12.800, which is about 55 nautical miles (102 km) north-northwest of Tripoli, Libya.

[2] The Regent achieved fame after it wove its way in April 1941 through two minefields and entered the Italian port of Kotor, in present-day Montenegro, to negotiate the release of the then British Foreign Minister to Belgrade, Ronald Campbell.

[4] After waiting for nine hours, a Yugoslav commander informed Browne that Yugoslavia had been overrun by German forces and Campbell was being held by the Italians at a small village called Herceg Novi, a short distance down the coast.

[2] In November, the British submarines Regent, Otus, Unique, Ultimatum, Ursula and Urge deployed to interdict convoys sailing between Italy and Tripoli.

[2] In January 1942, Regent deployed to Gibraltar, but then sailed to the Philadelphia Naval Shipyard, United States, for a refit, which began on 16 February.

In 2014, Regent's wreckage was believed found at a depth of 28 metres (92 ft) at 41°29′N 16°16′E / 41.483°N 16.267°E / 41.483; 16.267, some 10 miles (16 km) north of Barletta, on Italy's Adriatic coast.

she was moored up and her position was recorded by the Royal Navy while doing a survey of the area with the view of future amphibious landings.

One theory, which has gained credence, is that on 18 April Regent struck a mine north of Barletta, after attacking an Italian convoy.

[2] A second theory was that on 18 April the submarine was north of Monopoli, further along the same coast, where she fired a torpedo at the merchant vessel Balcic, but missed.

The Italian corvette Gabbiano was escorting Balcic and immediately launched a depth charges attack, which it was thought could have destroyed Regent.