The M113 armoured personnel carriers are American produced military vehicles that have operated in the Australian Army since 1964. An initial pair of M113s was purchased for trials purposes in 1962. Either 817 or 840 were acquired by 1979, comprising nine different variants. A long-running modernisation program that commenced in the 1990s resulted in 431 M113s being upgraded between 2007 and 2012. All of the upgraded M113s remain in service as of 2020.

In Australian service, the M113 has equipped armoured transport and reconnaissance units as well as mechanised infantry formations. It has also been used as a support vehicle by many other units. The type played an important role in Australia's commitment to the Vietnam War between 1965 and 1972. Some M113s were deployed as part of peacekeeping missions in Somalia during 1993 and Rwanda between 1994 and 1995. Larger numbers of M113s operated in East Timor from 1999 to 2002 and 2006 to 2008.

Despite the upgrade program, the Australian Army's M113s are now obsolete and they have not been included in recent deployments due to their vulnerability to attack. A project to replace the M113s with infantry fighting vehicles is underway, with a decision on the type to be procured scheduled for 2023. It is planned that the replacement vehicles will begin to enter service from 2025 and the M113s will be retired when this process is complete.

Acquisition

Trials In 1958, the Chief of the Australian Army's General Staff, Lieutenant-General Ragnar Garrett, initiated a program to modernise the Army's organisation and equipment so that it was compatible with those of Australia's allies, particularly the United States Army. This program included the acquisition of armoured personnel carriers (APCs), as well as FN FAL rifles, M60 machine guns, M2A2 howitzers, M40 recoilless rifles, L16 81mm mortars and radios.

The adoption of the pentropic organisation in 1960 led to a requirement for APCs to equip the Army's armoured units within the Royal Australian Armoured Corps (RAAC). This organisation included two APC regiments, the 12th/16th Hunter River Lancers and the 8th/13th Victorian Mounted Rifles; both were reserve Citizen Military Forces (CMF) units. Each regiment was authorised 119 APCs. A further two APCs were planned to be issued to each of the Army's two armoured regiments and nine were to form part of the equipment of the two divisional reconnaissance squadrons. The reconnaissance regiment in the pentropic divisions' combat support group was to have 25 APCs. The pentropic structure was abandoned in 1965, before M113s had been delivered in significant numbers.

A formal Weapons and Equipment Policy Statement specifying the Army's requirements for tracked APCs was issued on 26 June 1960. This document was very similar to a British War Office Policy Statement issued in the late 1950s. It called for the Army to acquire tracked APCs that were amphibious and could be carried by aircraft. These vehicles were to replace the Army's wheeled scout cars and APCs which had been purchased in the 1950s, as well as obsolete armoured fighting vehicles (AFVs) dating from the Second World War. It was believed that the wheeled armoured vehicles were no longer suitable, as the Australian Army expected that it would need to fight in tropical conditions in South East Asia. Tracked vehicles were preferred for these conditions as they had superior off-road performance, including in jungle terrain. The statement specified that the new vehicles would be used to equip the Army's APC, armoured and reconnaissance units. At this time the Army did not include any mechanised infantry units which were permanently issued APCs, and separate APC-equipped units were used to provide protected transport for light infantry.

The Weapons and Equipment Policy Statement included a requirement that potentially suitable designs be subjected to extensive trials in tropical conditions before an order was placed. The American M113, the British FV432 and the Canadian Bobcat were considered. The Bobcat was the least advanced and no prototype had been completed, so it was rejected before trials were conducted. After negotiations between the Australian and British governments between 1960 and 1962, the British Ministry of Defence (MOD) requested that Australia conduct a trial of the FV432 in tropical conditions. The Australian Army rapidly agreed to this request, and two FV432s were shipped to Australia, arriving in September 1962. These were prototypes, as the FV432 was yet to enter production. It proved simpler to acquire M113s for trial as the type had been in mass production since 1960. Two were ordered in 1961, and they arrived in Australia on 9 October 1962.

From November 1962 to April 1963, the two FV432s and two M113s were subjected to trials at several locations with different climatic conditions in the state of Queensland. The trials began with crew familiarisation and driver training on both types in the Innisfail area. Once this was complete, the four vehicles were driven to Mount Isa to conduct trials in hot and dry conditions. These included automotive and physiological tests, the latter of particular interest to the MOD. Testing in extreme heat during this phase found the M113's poor ventilation took a heavy toll on crew and passengers; one driver lost in two hours. The FV432's forced air ventilation system proved superior. At the conclusion of this stage of the trials, the vehicles were driven a further back to Innisfail for hot and wet trials at nearby Mourilyan. This phase included extensive driving through jungles and on sandy beaches, amphibious testing and being left unattended for 14 days. The M113 outperformed the FV432 in almost every aspect; its smooth sides and roof stowage proved far superior when driving through overgrown jungle, the lower track pressure and better track design proved superior on sand and it was significantly more waterproof. It was also found that the M113 required significantly less time to prepare for amphibious operations, though it was slightly slower than the FV432 in the water. The FV432's amphibious preparations included the removal of every inspection plate and the erection of a large rubber flotation screen; the latter was seen as a major drawback as it completely blocked the driver's vision and the rubber screen was easily punctured by debris or vegetation.

At the conclusion of the trials, the FV432s were shipped back to the United Kingdom. One was later used by the British Army for trials purposes during the development of the FV438 Swingfire. The M113s were retained by the Australian Army, which used them to trial several modifications to the type. Both were eventually transferred to the Royal Australian Armoured Corps Memorial and Army Tank Museum.

Purchase and deliveries

The trials demonstrated that the M113 was much better suited to the Army's requirements than the FV432, and accordingly the M113 was selected. Several improvements to the type were recommended before final acceptance. These modifications included the installation of a ventilation system and, in coordination with engineers from the vehicle's manufacturer FMC, a ventilation system unique to Australian vehicles was developed. Orders were placed during the 1963–1964 financial year. At this time, it was planned to retain the M113 in service until 1995.

The M113A1 variant was ordered for the Army, the first deliveries being scheduled for 1964. This vehicle had a crew of two and could carry up to eleven passengers. Its armour provided protection against small arms and shrapnel. While the original US Army M113s were powered by a petrol engine, the Australian Army selected the M113A1 variant that used the General Motors 6V-53 Detroit Diesel engine. This is a V-6 displacing 5.2 liters (318 cubic inches), developing up to @2,800 rpm and of torque @1,400 rpm. This was chosen because the variant had greater range and the diesel fuel it used was less likely to combust if the APC was damaged in combat. As the same engine was used to power buses in Australia, spare parts were also readily available. The Australian M113A1s were initially armed with a single pintle-mounted 0.5 inch calibre M2 Browning heavy machine gun.

In 1962 the Army decided that cavalry regiments equipped with lightly armoured vehicles would be its main armoured units. It was believed at the time that tanks were unsuited for the tropical environments the Army expected to fight in, and that lightly armoured vehicles would provide adequate support for the infantry. The structure of the cavalry regiments was established in 1964, the same year as the decision to abandon the Pentropic structure was made. They were to include three fighting squadrons, each with three troops equipped with APCs, a fire support troop and an anti-tank and surveillance troop. At the time the Army did not have any fire support vehicles; the M113A1 Fire Support Vehicle (FSV) later filled this role. In 1965 it was decided to structure the RAAC as armoured (tank), cavalry and APC regiments. The M113s were to be operated by RAAC personnel, and be treated as fighting vehicles rather than only armoured troop transports. The CMF armoured units were to be equipped with M113s for training purposes. In his history of the RAAC, Major General Ronald Hopkins judged that the cavalry regiment structure produced "handy" units with considerable mobility and firepower, but their effectiveness "rested on not being opposed by medium tanks or heavy anti-tank weapons".

Deliveries of the M113 began in 1964 but proved slow, the first bulk shipment of the type arriving in early 1965. The first vehicles to be delivered included specialist variants, including fitters vehicles (which carried maintenance personnel) and mortar carriers. M113s were initially issued to the Armoured Centre at Puckapunyal for crew training, which was conducted by US Army personnel at first. The type began to be issued to RAAC units on 19 March 1965. Priority was given to the Australian Regular Army's APC units, where the M113s initially replaced Alvis Saracen wheeled APCs. CMF units were accorded a low priority for M113s due to the need to allocate them to units involved in the Vietnam War, and some did not receive any until the late 1960s. Deliveries of the M113s were completed in 1979.

The planned cavalry and APC regiments were established in 1966. The 1st Cavalry Regiment was formed in January, and renamed the 2nd Cavalry Regiment later that year. The APC regiment was established as the 3rd Cavalry Regiment. The CMF 4th/19th Prince of Wales's Light Horse, 10th Light Horse Regiment, 2nd/14th Light Horse Regiment and 3rd/9th Light Horse (South Australian Mounted Rifles) were also converted to the cavalry regiment structure during 1966. The 4th Cavalry Regiment, a cavalry formation, was established in 1971.

M113A1 variants and modifications

M113A1 variants

The original orders of M113s included several variants in addition to the M113A1 APC: M125A1: These vehicles were based on the M113A1 and fitted with a single 81 mm mortar. The mortar was mounted inside the rear hull on a turntable, and racking was fitted inside the vehicle to carry mortar ammunition. The variant had a large hatch on the roof of its hull which the mortar was fired through. The M125A1 was armed with a M2 Browning for self-protection. M113A1 Fitters: These vehicles were also based on the M113A1 and were used to repair equipment in combat areas. They were fitted with a hydraulic crane on their roof capable of lifting an engine and transmission pack. The vehicles also carried tools, spare parts and technicians. They were armed with a M2 Browning. M113 Armoured Recovery Vehicle Light (ARVL): This variant was used to recover other vehicles from the field.