Realistically, to start preparing for a war with Japan from the 30s, the building up of the smallarms, artillery and automotive plants seems like the most immediate and viable way to go, with the goal of having it feed into a doctrine that leads to early adoption of the
jungle division system. Also, more resources into anti-aircraft weapons that can be deployed north. Getting to wartime aircraft and shipbuilding capabilities earlier is good, but I can't see this resulting in effective fighter planes and submarines being constructed here, which is really the strategic game changer IMO.
Everything else involves grand nation building and multilateral planning.
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When it comes to the subject of this Australian economic developmental autonomy people are raising here, my preferred solution is out of the scope of the thread's original what-if: it involves having Labo(u)r decisively losing the
1914 federal election, allowing the original Liberal Party to continue in office with majorities in both houses.
In that scenario Billy Hughes has no impetus or, IMO, even possibility of 'ratting' to the centre-Right, as they would just never take him if they'd continued in government under Sir Joseph Cook as PM and Sir John Forrest as treasurer. They would've had their own mandate to introduce, or fail to introduce, any kind of WW1 conscription. Even if we throw 'principle' into the mix, I'm pretty certain an Opposition leader Hughes simply decides to ignore his pro-conscription tendencies in 1916, like Chifley deciding against following his own fiscal conservative tendencies in the Labor split of 1931.
My feeling is that the OTL cross-party friendship Hughes and EG Theodore had, which actually brought down the Stanley Bruce Nationalist government in 1929, would have dominated Australian politics if they'd both been working within a united Labor throughout the twenties. Fwiw, to allow for the party stability needed to have this work, I'd handwave a Canadian CCF or NDP style party constitution for Australian Labor, which is also how the state trades hall councils relate to the national ACTU in the union movement, i.e. a non-adversarial relationship, one where splits and schisms aren't utterly debilitating.
Long story short, have a Hughes federal Labor government be in office during the twenties, have it be the ones who create the loans council, have it lose office in 1928 or 29 (as happened to the conservatives IOTL), but not before its started railway construction to Darwin; have Theodore sweep back into power in 1932 or 33 as PM, with Hughes as his external affairs minister who doesn't like appeasement (as per his views in OTL) and so wants to direct some of a Theodore New Deal towards heavy industry and defence infrastructure... then maybe we get the capacity to ramp up to producing effective fighter aircraft and subs after war comes, with the AltBeauforts and minesweepers already being in production by '39. Plus a single gauge rail link to Darwin not only from Alice, but maybe also from Mt Isa. Captain Cook graving dock also, by '41?
But like I said, a PoD that's decades before the 1930s international crises.