I am new here, and I do not know if this topic has been covered before. China, looking south towards south-east Asia, and further on to Australia, needs to watch its back if it contemplates an invasion of these regions. China has Russia to worry about, so can only allocate a fraction of its forces to any invasion south and south west. Japan was in a similar position in WW2. Australia, by contrast, does not need to watch its back. Further south is nothing but the Great Southern Ocean, so Australia can allocate all its military resources to its northward approaches. Australia is an island nation, so the Navy is the most important part of its defence. A hundred years ago, increasing naval strength was easy - buy more dreadnoughts. It is more complicated today; anti-ship missiles have replaced big guns, and anti-aircraft missiles protect against hostile aircraft. Submarines are a serious threat to any invasion fleet. Large multi wheel land based missile launchers are a possibility against hostile shipping closer to shore. Australia does not project much naval power, so does not need an aircraft carrier. So the shopping list is: Missile cruisers, say a billion dollars each. Submarines, say a billion dollars each. Maritime patrol aircraft, including airborne radar, say $50 million each. Anti-ship aircraft, using Australia as an unsinkable aircraft carrier, say $50 million each. Multi wheel anti-ship missile launchers, using the coastal roads, say a few million dollars each. A$15 billion is about 1% of Australia’s GDP, and defence spending is about 2% of our GDP. If defence spending went to 5% of GDP, then increasing our naval power makes an invasion expensive for potential invaders, mainly China, but also Indonesia. Germany tried to invade Britain in 1940, over a mere 30 km of sea, but abandoned the plan when Germany could not secure sea and air superiority The reverse invasion was D Day, and was a huge industrial effort. I remember Australia’s involvement in the Vietnam War, and I thought that the Australian emphasis on infantry activity at the time diverted public attention from the military reality of defending Australia.