Ambon first came under attack from Japanese aircraft on 6 January. Against the Japanese seaplane bombers, the limited Allied air defences held out, but on 24 January Japanese carrier-based Zeroes began appearing and eventually the remaining aircraft were withdrawn, having been completely out-classed. On 30 January, a Japanese fleet including two aircraft carriers and about 5,000 Japanese marines and soldiers reached Ambon. Although the Japanese ground forces were numerically not much bigger than the Allies, they had overwhelming superiority in air support, naval and field artillery, and tanks. In the belief that the terrain of the southern side of the island was too inhospitable for landings, the Allied troops were concentrated in the north. However, the initial Japanese landings were in the south, while other landings found the more lightly defended southern beaches. The Australians had been tasked with defending the Bay of Ambon, and the Laha and Liang airfields.