Battle of Tsimba Ridge

The Battle of Tsimba Ridge was an engagement of the Second World War involving Australian and Japanese forces. Part of the wider Bougainville campaign of the Pacific theatre, the battle occurred in the northern sector of Bougainville Island between 17 January and 9 February 1945, when the lead battalion of the Australian 11th Brigade—the 31st/51st Infantry Battalion—advanced towards the Genga River as part of a drive north to the Bonis Peninsula.

On the peninsula, an enclave of Japanese troops had established itself after withdrawing north following earlier engagements in the centre of the island throughout 1944–45. Coming up against heavy resistance along Tsimba Ridge, the Australians' advance was halted for three weeks as they fought to wrest control of the ridge from the defending Japanese from the 81st Infantry Regiment, whose strength was roughly equal to that of the Australians. The main Australian attack took place on 6 February, but it was not until 9 February that the Japanese completely withdrew from the position. Small-scale fighting in the surrounding area continued until 22 February. The next stage of the campaign saw the Australians take Ratsua as they sought to establish a defensive line across the base of the Bonis Peninsula between Ratsua and Ruri Bay.