HMS Sumar (FY1003) was a yacht purchased by the Admiralty of the United Kingdom during the Second World War converted to an armed yacht and equipped for anti-submarine warfare, replacing HMS Castle Harbour (which had been re-assigned to the Mediterranean in 1942) as the Royal Naval Examination Service vessel at Bermuda.

HMS Castle Harbour, a Bermudian tender which had been similarly commissioned, and which had been used by the Royal Naval Examination Service at Bermuda since the start of the war, was transferred to the Mediterranean, but sunk on transit on 16 October 1942 by the German submarine U-160.

On 2 June, 1942, Sumar (by then under the command of Lieutenant Gordon Emerson Kernohan, Royal Canadian Naval Voluntary Reserve) departed Bermuda with the United States Naval Operating Base Bermuda (the United States having been granted naval and air base leases in Bermuda by the British Government in 1939 and 1940)[7][8][9] tender USS Gannet (which had also been built by Todd Shipyards Corporation), under the command of Lieutenant Commander Frances Edward Nuessle, US Navy, in response to a distress call from the British merchant ship SS Westmoreland, which had been torpedoed by the German submarine U-566 220 nautical miles (410 km; 250 mi) northward of Bermuda.

Her commanding officer and other survivors tied together life rafts with wounded and clung to the sides in the heavy seas.

The dockyard rebuilt her for passenger service (reportedly to operate between Alexandria in Egypt and Marseille in France), and her new Greek owners (whose agent in Bermuda was William E. Meyer and Company Ltd; the ship having been placed on the civil register in Panama)[14] renamed her Horizonte Azul.

She departed Bermuda on the 3 August, 1946, with a delivery crew composed of a mix of British (Bermudian) and Polish nationals under Greek Captain Stratis Goulandria taking her to Gibraltar, where she arrived twenty-one days later.