At 8.30 pm on 8 February, Australian machine gunners opened fire on vessels carrying a first wave of 16 infantry battalions, totalling around 4,000 Japanese troops, towards Singapore Island, concentrating on the positions occupied by the 3,000-strong 22nd Brigade. While the artillery fired thousands of rounds in response to support calls, confused and desperate fighting raged throughout the evening. Eventually the increasing Japanese numbers, poor siting of defensive positions, and lack of effective communications, allowed Japanese forces to exploit gaps in the Australian lines. By midnight the two 8th Division infantry brigades, the 22nd and 27th, were separated and isolated, and the 22nd had begun withdrawing towards Tengah. By 1:00 am, further Japanese troops – bringing the total to 13,000 – had begun landing and as the main Australian force was pushed back towards Tengah airfield, small groups of troops that had been bypassed by the Japanese fought to rejoin their units as they had withdrawn toward Tengah airfield. Around dawn on 9 February a further 10,000 Japanese troops landed, and as it became clear that the 22nd Brigade was being overrun and it was decided to form a secondary defensive line to the east of Tengah airfield and north of Jurong.