First Carrier Division
The B6N "Tenzan" began reaching front-line units in August 1943 in small numbers. The intent was to gradually replace all of the B5N "Kate" torpedo bombers then operating aboard the carriers of the Third Fleet at Truk Atoll in the Caroline Islands. However, the B6Ns were prematurely committed to battle when increased Allied naval activity in the Solomon Islands indicated a likely invasion at Bougainville. In response to this threat, the IJN initiated Operation Ro. This involved reinforcing land-based air units at Rabaul with 173 carrier aircraft from First Carrier Division ("Zuikaku", "Shokaku" and "Zuiho"), including forty B6Ns. These aircraft were flown from Truk to Rabaul between 28 October and 1 November.