The invasion of Malaya began shortly after midnight on 8 December 1941. Two hours later, No 1 Squadron RAAF, based at Kota Bahru, in north-east Malaya, was airborne. Soon, two of the Hudson bombers were shot down, and Flying Officer John Dowie, the only survivor of the two crews, became the first Australian prisoner of war captured in Malaya. That same morning, an Australian corvette, HMAS Maryborough, patrolling off south-east Malaya, intercepted a Japanese fishing boat, the Fukuyu Maru, the first Japanese vessel captured by an Allied warship. On the west coast of Malaya, No 21 Squadron RAAF at Sungei Patani suffered devastating air raids and by the evening of 8 December both Sungei Patani and Kota Bharu airfields had been evacuated.
On 9 December, No 8 Squadron, which also had gone into action, was evacuated from Kuantan airfield. On 10 December, the destroyer HMAS Vampire became the first Australian ship in action against the Japanese when HMS Repulse and HMS Prince of Wales were sunk off the east coast of Malaya by enemy aircraft. Vampire and the three other escorting destroyers were able to rescue over 2000 survivors from the two British ships.
On the ground, British and Indian troops were also pushed back during December and early January. Some Australian transport and ambulance drivers saw early action alongside Indian troops, but the first major Australian battle was not until 14-15 January 1942. A company of the 2/30th Battalion, commanded by Lieutenant-Colonel Frederick Galleghan, mounted an ambush which cut down hundreds of Japanese soldiers riding bicycles through a cutting and over a bridge on the Sungei Gemencheh river. Their plan was to withdraw and let the main battalion group at Gemas fight the main battle. As the ambush party withdrew, they found themselves encircled by Japanese patrols but most managed to get through. The battle for Gemas raged that night and next day and on the afternoon of 15 January the Japanese called in aircraft and tanks and the Australians withdrew.
On 15 January 1942, the 45th Indian Brigade on the west coast, defending the line of the Muar River, was also involved in a battle with the veteran Japanese Imperial Guards Division. Two battalions from the 8th Australian Division were despatched as reinforcements: the 2/29th and the 2/19th Battalions. The Indian brigade was pushed back towards Bakri where, north of the village, the 2/29th and some gunners of the 4th Anti-Tank Regiment provided blocking action. Japanese forces penetrated between the 2/29th and the 2/19th at Bakri. The 2/29th had to fight their way back to Bakri. The Australians held on to enable some Indian troops to also reach them, but they came under heavy ground and air attacks. Nearly all staff at the 45th Indian Brigade's Headquarters were wounded or killed when a bomb hit their headquarters. Lieutenant-Colonel Charles Anderson, Commanding Officer of the 2/19th Battalion, took command of all troops and decided to withdraw towards Parit Sulong. While he waited for a missing Indian unit, the Australians became heavily engaged front and rear, and on 20 January they had to start fighting their way south through Japanese positions. Anderson's men attacked to re-open their escape route, and by the early morning of 22 January they had reached the village of Parit Sulong, but were in a parlous situation. A strong enemy force blocked their escape route, many of the Australian and Indian troops had been killed or wounded, and a British relief force was blocked. Anderson was forced to order his men to escape in small parties through the countryside, first destroying all guns and vehicles, and had to leave the wounded behind. Just 271 members of the 2/19th and 130 of the 2/29th - less than a quarter of the Australians at the start of the battle - escaped. For his valour and leadership, Lieutenant-Colonel Anderson was awarded the Victoria Cross, the highest decoration for valour.
The 110 wounded Australians and 40 wounded Indians left behind at Parit Sulong were brutally stabbed and incinerated by the Japanese with just one man, badly hurt, surviving to tell the story at war's end.
Over on the west coast, on the night of 26-27 January, the Australian 2/18th Battalion successfully ambushed a Japanese force at Jemaluang, south of Mersing. Under the command of Lieutenant-Colonel Arthur Varley, supported by two batteries of the 2/10th Field Regiment, the 2/18th sprang their ambush between 2 am and 3 am. Brigade headquarters ordered Varley to withdraw after first light, after they encountered heavier attacks from the enemy. Nevertheless, the Australian action was a stunning success which turned the Japanese force inland, rather than continue pushing south along the west coast. The 2/18th lost 98 troops killed or missing, but Japanese losses were heavier.
Air and naval forces also continued to be heavily engaged. Hudson bombers of Nos 1 and 8 Squadrons RAAF bombed enemy positions, and patrolled out to sea, and Nos 21 and 453 Squadrons RAAF with Buffalo fighters, outclassed by Japanese 'Zero' fighters, fought on. Other Australians flew in British squadrons, some in outdated Vildebeest biplane torpedo-bombers that lost heavily. On 27 January, HMAS Vampire, together with HMS Thanet, took part in an attack on a superior Japanese surface force off Endau on the east coast. The British ship was lost during the battle and HMAS Vampire only narrowly escaped being sunk. Australian corvettes endured many air attacks escorting incoming convoys, one of which included the cruiser HMAS Hobart.
By 30 January 1942, the Japanese XXV Army had advanced to the Strait of Johore at the southern tip of Malaya. The weary British, Australian and Indian troops made their way over the Causeway to Singapore Island and on 1 February, after the last man had crossed, engineers blew up sections of the Causeway to isolate the island.