When she finally rejoined the Home Fleet in November 1942, under the command of Captain (later Admiral Sir Frederick) Parham, HMS Belfast was the largest and arguably the most powerful cruiser in the Royal Navy. Not only had she been 'bulged' amidships, increasing her standard displacement to 11,500 tons and significantly improving her stability, but she had also been equipped with the most up-to-date radar and fire control systems. As a result, she was soon in the forefront of Britain's naval war in the Atlantic; as flagship of the Tenth Cruiser Squadron, responsible for providing close range heavy cover for the Arctic convoys taking supplies to the Soviet Union.
On 21 February 1943, wearing the flag of Rear-Admiral (later Vice-Admiral Sir Robert) Burnett, HMS Belfast left Iceland for the Russian port of Murmansk in support of Convoy JW53. Although the Germans failed to prevent the convoy from reaching its destination, hurricane force gales caused severe damage to warships and merchant vessels alike.
Apart from occasional offensive sweeps with the battleships and aircraft carriers of the Home Fleet, HMS Belfast was to spend most of 1943 engaged on similar duties in the icy waters of the Arctic.
Between August 1941 and the end of the war, a total of 75 convoys made the perilous journey to and from north Russia, carrying four million tons of supplies, including 5,000 tanks and 7,000 aircraft for use by Soviet forces fighting against the German Army on the Eastern Front. The merchant seamen showed true heroism during their long sea passages in convoys, during which half or more of the ships could be sunk before safety was reached.
During the Second World War the British merchant navy lost over 30,000 men and 5,150 Allied merchant ships were sunk as a result of enemy action.