HMS Unity was a U-class submarine, of the first group of that class constructed for the Royal Navy. The submarine entered service in 1938 and performed war patrols during the Second World War. On 29 April 1940, Unity was accidentally rammed and sunk in Blyth, Northumberland's harbour.

Unity was built by Vickers Armstrong, Barrow-in-Furness. She was laid down on 19 February 1937 and was commissioned on 5 October 1938.

At the onset of the Second World War, Unity was a member of the 6th Submarine Flotilla. From 26–29 August 1939, the flotilla deployed to its war bases at Dundee and Blyth. She served in home waters in the North Sea, making a failed attack on the German submarine U-2.

She rescued the survivors of Dutch fishing vessel Protinus on 25 March 1940.

On the 11th of April 1940, at AN3446, Unity was spotted by U-5, a German Type IIa coastal submarine commanded by Kapitänleutnant Lehmann. U-5 fired a G7a (T1) steam powered torpedo at the Unity, which subsequently saw the bubble trail and proceeded to crash dive in heavy seas. U-5 followed suit in an attempt at an underwater shot with a G7e (T2) electric torpedo. However contact was lost and Unity managed to escape unharmed.

Unity sailed from Blyth on 29 April 1940 to patrol off Norway, where she collided with the Norwegian ship Atle Jarl, sinking five minutes later. Two members of her crew, Lieutenant John Low and able Seaman Henry Miller, gave their lives by remaining behind in the flooded control room so that their shipmates could escape from the sinking vessel.

The wreck is accessible by technical divers, lying at a depth between 48 and 55 metres (157 and 180 ft) off the Farne Islands.

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55°13′N 1°19′W / 55.217°N 1.317°W / 55.217; -1.317