Malaya (the mainland component of present-day Malaysia) was a key British colony prior to the Second World War. Economically, it was the source of large quantities of natural resources, particularly tin and rubber; and strategically it provided a large defensive barrier to any landward advance on Singapore and its naval base - the cornerstone of British power in the Asia-Pacific Region.
The Japanese Army was well aware of the significance of Malaya and began planning for an invasion in October 1940. It launched this operation with landings on the north-eastern coast of Malaya, at Kota Bharu, at 1.45 am on 8 December 1941; occurring 40 minutes earlier than the raids on Pearl Harbour this was the first major Japanese attack of the Second World War. Soon after, Japanese troops were also landed at Patani and Singora on the south-eastern coast of Thailand. The Kota Bharu landings developed into a drive down the eastern side of the Malay peninsula, while the troops landed in Thailand advanced down the western side. Badly organised defences in northern Malaya proved no match for the Japanese and in early January the British command decided to concentrate their efforts in southern Malay region of Johore.
The operations in Johore were entrusted to the 8th Australian Division, with an Indian brigade attached, under the command of Major General Gordon Bennett. Despite several local tactical successes by Australian units at Gemas (14 January), Bakri (18-19 January) and Jemaluang (27 January), the Australians were not able to hold the Japanese and the withdrawal towards Singapore continued. On 31 January 1942 the last British Commonwealth troops withdrew across the Straits of Johore to Singapore, and a large gap was blown in the causeway behind them.
The rapid success of the Japanese advance was due to several factors. The first was that they had complete control of the air. Although British Commonwealth squadrons were deployed forward in Malaya, their obsolete aircraft were easily destroyed by the Japanese. The need to protect the airfields also severely limited the freedom of action of commanders on the ground early in the campaign. Secondly, the Japanese units had extensive operational experience that manifested itself in efficient and well-executed battle drills. Contrary to popular belief, the Japanese were not overly experienced in jungle warfare. They utilised Malaya's roads to ensure a speedy advance (during the Malayan campaign they advanced on average 15 kilometres per day) and when they met with opposition, sought to outflank it through the jungle. The defensive tactics of the British and Commonwealth forces were ill-suited to this approach, and, also heavily dependent upon the roads for their mobility, they were usually forced to withdraw. On the west coast the Japanese also used watercraft to facilitate outflanking moves. In the case of the 8th Australian Division, operations were also seriously handicapped by severe disharmony between Bennett, his staff, and his subordinate commanders. With the loss of Malaya, no more than a kilometre of water separated the Japanese from Singapore, and any hope of successfully defending Singapore was lost.