Some Australian units were issued with M1 steel helmets, both US and Australian made during the Vietnam war. Units known as ‘Mini Teams’, which were a type of small counter mine unit, were issued with M1 steel helmets and US Flak jackets. Mostly the Australian Infantry wore the British Pattern Bush Hat or’ Giggle-Hat’, later replaced by the Australian made type. This was part of the military uniform of the Australian Army and was to be worn at all times on operations and was not to be altered. The Australians wore the Giggle Hat as it was light, kept the sun and heat off in the humid conditions, and made for a ‘soldierly appearance’. The weight and bulk of the M1 Steel helmet limited its value to Australian soldiers on operations due to the nature of the Australian way of conducting war. The US style was considered loud, noisy and reliant on tactical mobility and fire support. In contrast the Australian method was to disperse over a wider area and patrol silently and cautiously. The Americans were conducting a conventional ‘big war’ and the Australians were conducting counter-insurgency, patrol war. The Australian army was not reliant on the same tactical mobility used by the Americans, and reducing the ‘soldiers load’ was a priority. Extra weight reduced the soldier’s mobility, energy and reaction time. The Australian report ‘Infantry Battle Lesson from Vietnam’ notes: “Carrying a heavy load used energy that should have been available for fighting.” This is an effect of the type of ‘patrol war’ the Australians were engaged in. The steel helmet in this case, had more drawbacks than positives. It offered protection only from shell splinters and blast waves, but added considerable weight, bulk and heat, reducing the solders combat effectiveness in the particular type of war the Australians were undertaking. The Australians had considerable experience in counter insurgency and jungle combat in Malaya and Borneo in the 1950’s, and developed tactics based on two basic infantry principals, patrol and ambush. Working with the Americans, who at the time were using large scale airborne assaults, the previous learnings were going unused. Frustrated with this, the Australians sought independence from the US operations and took over the Tactical Area of Operational Responsibility in Phouc Tuy province in 1966. Here the Australian tactics and experience were more successful. Other units and forces that also did not consistently wear helmets these included: The NVA, The VC, the SASR, LRRP, SEAL teams and MACV SOG. These are all units where reducing the soldiers load was critical, due to the nature of their operational approach. As a result, some Australian units would wear a coloured tape in their bush hats, to differentiate them from enemy units. You can read a previous answer of mine here about why the NVA did not widely adopt a steel helmet during the war.

Sources:

Australian Army Training Information Bulletin Number 69, Infantry Battalion Lessons from Vietnam, 1965-71 (pub. 1988).

Vietnam Anzacs by Kevin Lyles.

Historical Documentation of the Infantry Helmet Research and Development by Charles Houff and Joseph Delaney.