Thank you for your response.Sheridan is completely wrong - and as been said above, most of this lays at the feet of Army. Oops...
Everything above provides the justification for armour; let me have an attempt at strategically justifying it. I'll apologise now for length and beg your indulgence for (a) length and (b) accidently telling you to suck eggs
DSU para 1.3 - 1.6 highlight how the security situation within the Indo-Pacific is degrading, with Great Power competition and 'grey zone activities' {} increasing. Para 1.6 - 1.8 highlight how there is an effective arms race within the region, with multiple nations conducting military modernisation. Para 1.12 sums it up:
Para 1.17 - 1.20 further define the security situation in the region as degraded and under increased risk beyond 'simple' State-on-State conflict. As para 1.20 says:
Chapter 2 hits the key points, but I'll note that while there is a focus on the Indo-Pacific region, para 2.11 highlights our need to be able to respond at further distances if needed (although not an equal level force design determinant, it is still Government direction). Additionally, para 2.13 directs, among others, increased self-reliance for deterrence and enhance the lethality of the ADF.
Now it boils down to the three key bulwarks of the DSU: shape, deter, respond. Para 2.14 onwards define this, but key points for this discussion are:
Shape - build new, and strengthen existing, partnerships, strengthening sovereignty and resilience to coercion, cooperative defence activities is fundamental to our ability to shape our strategic environment, be prepared to lead coalition operations
Deter - Australia take greater responsibility for our own security, deliver deterrent effects against a broad range of threats.
Respond - The ADF must be better prepared for such conflict if deterrence measures fail, or to support the United States and other partners where Australia’s national interests are engaged, enhance the lethality and readiness.
So what does this mean for the Land Domain? Firstly, to shape and lead we need a credible military. The reality is that coalition leaderships and credibility still (rightly or wrongly) fall upon the land forces, especially in this region. So the land force needs to be credible, meaning its well trained and equipped to fight a broad range of threats, including China (although that is less relevant - as chap 1 highlights, war with China is but one possibility). A land force that is credible, trained and equipped means that it has some deterrence effects, and here you get into another aspect. The land force needs to be able to hit hard. And, as much as possible, from range and at any time. This demands firepower, and heavy firepower at that. It also demands excellent communications and the ability to respond quickly, be it tactically or strategically. A land force that can do these can respond, but note that we have to respond across a range of scenarios.
So the land force needs to be credible, flexible, resilient, protected, have good chunks of firepower and comms. This could be anything - until you take a step back and consider how any army fights.
The reality of any element within the land force is that they all have flaws. Infantry is squishy, slow and weakly armed; artillery vulnerable at range and if it can't see; armour vulnerable in close terrain and if you get in close; engineers are just plain offensive {
Now, like strawberries and cream, soldiers and beer or dogs and happiness, the two arms that cover each other the best are armour and infantry. Almost every single negative for a tank is a positive for infantry and vice versa. Which means that everywhere you put a grunt, you want a tank. Well, a Coy of grunts and a Tp of tanks - they don't fight alone. Without tanks your infantry can only be used for the lightest of duties. Now this does demand other attributes - logistics and engineers - but we return to the DSU we find they also contribute to the other parts of resilience and shape, both trades are essential to building partnerships and responding to threats. Furthermore, nothing can provide the shock action, firepower, mobility and persistence of a tank - all of which are much more than the sum of its parts.
So to meet the Government directives and you need tanks. They give credibility, lethality and persistence in a way nothing else can. There may be a replacement the future - but not now.
But where to use them (the second half of your question)? Well, the DSU answer is yours - wherever there are infantry and there is a threat. @Volkodav says it best here, but if the threat has tanks you need the same and if they don't you have over match. The statistical answer is that studies with and without armour consistently show that adding tanks to the mix in all forms of warfare from COIN to peer conflict mean you save lives, mostly infantry. This is for Russian, European, Middle Eastern, American and Australian experiences - any nation that practices combined arms warfare. In Vietnam we saved lives with tanks, and in Afghanistan the Canadians found that was the case. In both these conflicts we can even compare before and after tanks.
But if committing tanks saves lives, why not us in AFG or IRA? Two things - outdated tank (Leo 1) that was not survivable and politics. Every force we commit is a political decision, and none of the governments of the day wanted a big Australian presence or one that was in enough combat to take casualties. So it was more palatable to adopt lower threat areas and restrictive ROE than deploy tanks. Plus the appearance of sending tanks wouldn't have fit with either Party's goals of downplaying our involvement; same as why Tiger didn't go.
Fundamentally, to look at limited wars of choice and say 'we didn't use them so don't need them' is really bad. We'd have never bought F/A-18's if that was the case. JTF's are politically built, and just because there is a threat doesn't mean that the ADF will get their way in what they send. I'd argue that the job the F/A-18's were doing in the MEAO recently could have been done by almost any propeller plane and they weren't engaged in air-to-air combat, but you'll never see me saying the RAAF hasn't fought since 1952 so we don't need fighters. Tanks allow that flexibility, the government can chose not to send them. Better that than committing forces and realising we need tanks - but don't have them. It also gives the Government more options as to how to respond to conflicts, or even if they do in the first place.
Overall / TLDR - the Government has directed the ADF to be credible, lethal and able to respond. The tank is a critical part of the Army's contribution to these aspects that cannot be replaced by any other system. They literally save lives; you should deploy them anywhere there is a threat armed with more than a rifle and there are Australian or friendly infantry. And finally, decisions to use assets previously should not be sued for force design in the future as they are political, not capability based.
My lack of land warfare education has been somewhat improved.
