The Jungle division was a military organisation adopted in early 1943 by the Australian Army during the Second World War. This organisation was a much lighter version of the standard British-pattern infantry division used during previous campaigns in the deserts of the Mediterranean and Middle East Theatre fighting the Germans and Italians in 1940 and 1941 and was optimised to meet the needs of jungle warfare against the Japanese in the South West Pacific Area. Jungle divisions were smaller and had fewer heavy weapons, vehicles and support units than the British-pattern division previously used and had an establishment of just 13,118 men, approximately 4,000 fewer than a standard division. The bulk of the reduction occurred among the administrative, transport and artillery units. The conditions that prevailed in the South West Pacific Area led the Australian Army to initially convert five infantry divisions to Jungle divisions, although this was later increased to six. Divisions converted to the jungle organisation included three Militia divisions: the 3rd, 5th and 11th and the three Australian Imperial Force (AIF) divisions: the 6th, 7th, 9th. Despite some modifications, this re-organisation proved successful during later Australian operations in New Guinea, New Britain, Bougainville, Aitape-Wewak and Borneo in 1944–1945.
Reorganisation of the Australian Army, 1943
The changing nature of land warfare during the Second World War led to significant changes in the composition of Australian Army units. The success of German mechanised units during the invasions of Poland and France convinced Australian defence planners that the Army required armoured units, and these began to be raised in 1941 when the 1st Armoured Division was formed. The two Militia cavalry divisions were first motorised and then converted into armoured divisions in 1942 and the 3rd Army Tank Brigade was formed to provide support to the infantry. However, in response to the growing Japanese threat Australian forces were concentrated in the South West Pacific Area and between 1942 and early 1943 the divisions of the Australian Imperial Force (AIF) had fought using the standard British Army organisation they had adopted during previous campaigns in the deserts of North Africa and the Middle East fighting the Germans and Italians in 1940 and 1941, while the Militia divisions used a 1941 Australian organisation which included a headquarters company, four rifle companies and a machine-gun company in each infantry battalion. Yet the early campaigns suggested that the existing organisation was unsuitable for jungle warfare and as a result of the changing operational environment in February 1943 Land Headquarters identified the need for three different types of division: armoured divisions, standard infantry divisions and jungle infantry divisions.
The jungle division organisation operated on reduced manpower and had fewer heavy weapons, vehicles and support units than the British-pattern division previously used, with the main imperatives being "manpower, transport, and communications." As many administrative personnel as possible were also removed from the divisional structure, while fewer vehicles also meant a reduced requirement for maintenance personnel and reduced logistical support. Each battalion was reduced in size and placed on a new "tropical war establishment", the anti-aircraft and carrier platoons were disbanded, and the latter converted into a medium machine-gun platoon of four Vickers machine-guns, while the number of 3-inch mortars was increased from six to eight. Equally while the standard division contained a large number of motorbikes, trucks and mechanised vehicles, such transport was of limited use in the rugged, roadless jungles and the muddy tracks of the South West Pacific. To this end each rifle company was restricted to just one jeep and trailer, relying instead on "foot mobility" and supported logistically by native carriers rather than vehicles, as well as by air transport and supply dropping. In addition to reducing the number of vehicles, most trucks were replaced by light vehicles, as these were able to more effectively traverse narrow tracks in difficult terrain, and could be manhandled across mud, soft sand and creeks if required. Following the reorganisation each infantry battalion consisted of a battalion headquarters, four rifle companies each of three platoons, and a headquarters company consisting of signals, machine-gun, mortar, anti-tank, pioneer and administration platoons. It had an establishment of between 800 and 850 men.