As the principal Far East base, Sydney would need submarines, boom defences, and forts covering its approaches. Protection would have to extend to the commercial harbour and civilian population as well as the dockyard. Better transport links to Canberra would support the larger establishment and its command responsibilities. A joint British and Australian headquarters would need a fleet commander beneath a combined commander-in-chief, probably an Admiral of the Fleet. That standing hierarchy could alter the later ABDA Command, especially if substantial British naval forces survived to join it. The historical submarine penetration of Sydney illustrates a risk these expanded defences would have to address.
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Sydney needs layered defence for the naval base and city
Defending Sydney would extend beyond the dockyard to the civilian harbour, while the base would require better transport links and a senior joint headquarters.