'Ro' (i) was the Japanese reinforcement of their base area round Rabaul in New Britain with aircraft delivered by aircraft carriers in anticipation of the US 'Cherryblossom' offensive against Bougainville island in the central part of the Solomon islands group (30 October/1 November 1943).
The Japanese feared that the loss of this island and its several air bases would open the way for a steadily heavier bombing effort against Rabaul on New Britain island by Lieutenant General George C. Kenney’s 5th AAF (the air element of General Douglas MacArthur’s South-West Pacific Area command) with escort provided by fighters of Rear Admiral Marc A. Mitscher’s Air Command Solomons, which was the land-based air element of Admiral William F. Halsey’s South Pacific Area command.
At this time Vice Admiral Jinichi Kusaka’s 11th Air Fleet in New Britain had only some 200 aircraft, and in 'Ro' another 173 aircraft (82 fighters, 45 dive-bombers, 40 torpedo bombers and six reconnaissance aircraft) were delivered from the stocks of Admiral Mineichi Koga’s Combined Fleet.
'Ro' was scheduled to start on 28 October, but at this time the Combined Fleet's plans were in disarray in the aftermath of an abortive sortie from Truk atoll on 5 October to try to intercept a US carrier task force, which had sortied from Pearl Harbor and was believed wrongly by the Japanese to be preparing for an attack on Wake island. The aircraft were finally transported by Vice Admiral Jisaburo Ozawa’s 3rd Fleet (fleet carriers Zuikaku and Shokaku and light carrier Zuiho of the 1st Carrier Division, and fleet carriers Junyo and Hiyo and light carrier Ryuho of the 3rd Carrier Division), and were unloaded on 1 November.
While returning to Japan after 'Ro', Junyo was torpedoed and damaged by the submarine Halibut on 5 November.
Thus completed successfully, the operation had been inspired by a similar undertaking organised by Admiral Isoroku Yamamoto at the end of March 1943 in preparation for 'I' (ii), when more than 100 aircraft and their crews had been unloaded from the fleet carriers of Ozawa’s 1st Carrier Division of the Combined Fleet to bolster the strength of the 11th Air Fleet in desperate efforts to strike as the growing US base areas in New Guinea and the Solomon islands group.