This was made in conjunction with landings at Pattani and Songkhla in Thailand, where units then proceeded south overland across the Thailand-Malayan border to attack the western portion of Malaya.

The Japanese also used bicycle infantry and light tanks, which allowed swift movement of their forces overland through the terrain that was covered with thick tropical rainforest.

By mid-January the Japanese had reached Johore where, on 14 January, they encountered troops from the Australian 8th Division, commanded by Major-General Gordon Bennett, for the first time in the campaign.

Bennett allocated the weak 45th Indian Brigade (a new and half trained formation) to defend the river's South bank but the unit was outflanked by Japanese units landing from the sea and the Brigade was effectively destroyed with its commander, Brigadier H. C. Duncan, and all three of his battalion commanders killed.

Following the successful capture of Malaya and Singapore, the IJA 25th Army served primarily as a garrison force for the occupied territories.