You're correct we are screwed without the US but the US always has "self-interest" overiding its AUKUS obligations in my opinion. Plus if we are to be deigned by the US, to be allowed, one day down the track, to buy a second-hand nuclear sub, it will be hard to find a crew of Aussies capable and willing to crew it. Plus if I google Chinese low-Earth orbit satellites I soon learn subs are trackable nowadays. Our subs, when and if we get them, have to surface, or at least up-periscope, 12 times on average between capital cities to recharge batteries even in nuclear subs, causing a v-shaped bow wave and mathematic programs can predict when and where this has previously occurred and will most probably happen again next time. The subs would be sitting ducks.
