During the initial part of the Second World War, Newcastle engaged and badly damaged two German destroyers off Brest. She also set a record during this period by staying at sea continuously for 126 days. On 23 November 1939, Newcastle encountered the German small battleships and but they escaped in bad weather before other ships could come up. Newcastle was involved in an abortive action under Vice-Admiral James Somerville on 27 November 1940 against the Italians at Cape Spartivento. After operating against blockade runners in the South Atlantic, the ship was sent to the East and then redeployed to the Mediterranean as part of Operation Vigorous, from Alexandria to Malta in June 1942. Four days out, Newcastle was torpedoed by the German E-boatS-56, on 15 June, blowing a complete hole through her bows. The crew saved the ship, which returned at to Alexandria, where she could not be fully repaired but was offered facilities to make her own temporary repairs. This meant building an additional wooden bulkhead, strengthened by concrete, behind the damage. This bulkhead had to be replaced at ports in India, Ceylon, South Africa and Brazil, before she finally arrived in October at Brooklyn Navy Yard, New York, where new bows were built by March 1943. From New York she sailed to Plymouth and then on to join the Eastern Fleet at Ceylon, and acting as the lead ship of the 4th Cruiser Squadron. During her time with the Eastern Fleet, Newcastle participated in the bombardment of numerous Japanese-held islands and supported the British Fourteenth Army in their campaigns in Burma.
Postwar
After the war, the cruiser was given an extensive modernisation in 1951-2, with a new bridge, New Mk 5 40 twin 40mm light AA armament and Type 275 radar to control its twin 4 inch guns and took part in the Korean War - acting as a flagship and providing naval gunfire support to UN forces. Newcastle also served during the Malayan Emergency in the later 1950s, shelling Malayan Communist targets in June and August 1955 and again in December 1957.
Decommissioning and disposal
Newcastle was decommissioned and sold for scrap in 1959, and subsequently broken up at Faslane.