With the end of the National Service scheme in November 1959, came the desire to modernise the Army and restructure it to enable better integration in operations with the forces of Australia's main ally, the United States. As a result, the Army was reorganised on a new divisional structure, called the Pentropic Division. The US Army had experimented with a Pentomic divisional structure, based on five battle groups. The core element of each was a significantly enlarged infantry battalion, to which was added elements of supporting arms. This organisation, which was the blue print for the Pentropic arrangement, eliminated the intermediate-level brigade headquarters. Implementation of the Pentropic divisional structure commenced in 1960.¹⁴⁹

The restructuring of the Army, particularly the CMF infantry battalions, to form the new battle groups, involved the disbanding of many old units with historical links going back to the Sudan, South Africa and the two World Wars, as well as severing traditional ties with their local communities. The new organisation presented a complex command and staff organisation as well as a number of difficulties at lower levels. The US Army abandoned its experiment in 1961, however the Australian Army persevered with the Pentropic structure until November 1964.¹⁵⁰

One significant complication was the requirement to maintain an RAR battalion with the BCFESR in Malaya (Malaysia after 1963) on the standard British Commonwealth battalion structure, whilst all other battalions were on the enlarged Pentropic structure. This resulted in battalions having to be reorganised for service in BCFESR. Reversion to the previous Tropical Warfare divisional - and battalion - structure was effected in 1965, with some restoration of the old identities of the original CMF battalions.¹⁵¹