fourth war patrol. May–June 1943 From 14 May to 8 June 1943, Blackfish remained at Rosneath undergoing upkeep. During that time her crew received nine days of shore leave. On 2 June, she carried out local training, during which she conducted gunnery exercises and approaches with a British S-class submarine. On 3 June 1943, Blackfish returned to Rosneath. Fifth war patrol Blackfish′s fifth war patrol began on 8 June 1943 with her departure from Rosneath in company with Barb and the British patrol vessel HMS Cutty Sark. During the patrol, Blackfish spent long hours submerged with no exercise and limited food selection for her crew, which contributed to some illness among the crewmen. She sighted some merchant ships on 4 July 1943. On 5 July she received orders to return to the United States. She moored to Pier 15 at Naval Submarine Base New London in Groton, Connecticut, on 26 July 1943, concluding her fifth war patrol. July–October 1943 Upon her arrival at Groton, Blackfish underwent repairs, during which she replenished her supplies and her crew conducted training for their upcoming deployment to the Pacific for the war with Japan. With her repaits concluded, she set out for Brisbane, Australia. Upon reaching the Panama Canal Zone, she transited the Panama Canal and briefly conducted training in Panama Bay before continuing her journey. She arrived at Brisbane in September 1943 and spent three weeks undergoing a refit there. Pacific operations Sixth war patrol On 19 October 1943, Blackfish set out on her first war patrol in the Pacific and sixth overall, headed for the waters around New Guinea, the Solomon Islands, and the Bismarck Islands. En route to her patrol area, she conducted multiple night radar training exercises on 20 October with her escort, the submarine rescue vessel . The two parted company on 24 October. At 05:13 on 26 October Blackfish arrived at Tulagi in the Solomon Islands and moored to an oil barge for fueling. On 27 October 1943, she rejoined her escort and got underway again at 06:00. While assigned to a scouting line on 3 November 1943, Blackfish was on the surface when she encountered a Japanese convoy of two merchant ships, which her crew estimated at approximately 4,000 to 6,500 gross register tons, escorted by one patrol boat. Because Blackfish was patrolling along a scouting line, there was some question as to whether or not she