The large Lockheed Martin SPY-1D radar panels see for at least 200 kilometres in every direction.

There is a forward-pointing satellite dish, the fire control radar, which "paints" a target. The circular "identification, friend or foe" sensor speaks pretty much for itself.

Everything is linked into the Aegis combat system, the warfighting brains of the ship.

"Aegis will determine the best option for dealing with the threat at hand. Once it's done that, they [the ship's operations room] will initiate the launch to eliminate the threat," the officer told Fairfax Media said.

It is this cutting-edge system, also made by the US giant Lockheed Martin, that has caused excitement this week because the Turnbull government, by announcing that Aegis will play a central role in the planned fleet of nine new naval frigates, signalled it considers one of the chief threats in the future to be ballistic missiles.

It comes amid the almost weekly threatening gestures made by rogue North Korea, though as some well-placed sources at the Navy's high-level Seapower conference in Sydney last week pointed out, China and Russia present larger and longer-term missile concerns. Indeed the ability to hit things from great distances is improving and it is proliferating around the world, particularly in the Indo-Pacific region.

Crucially, the new frigates and the Hobart-class destroyers combined won't be able to defend Australia from intercontinental range missiles - nowhere close. The Aegis announcement is one step, experts stressed, if an important one, down the road of missile defence. It means we're getting squarely in the game.

"There's no doubt that Australia's capability for ballistic missile defence will improve markedly when these ships [the new frigates] are delivered," wrote Andrew Davies, a senior analyst at the Australian Strategic Policy Institute, on the institute's blog on Thursday.

He continued: "But don't throw away those bomb-shelter plans just yet - we aren't going to have a national defence system anytime soon."

Defence Minister Marise Payne, in an interview with Fairfax Media, said she discussed ballistic missile defence with US Secretary of Defence James Mattis on a recent visit to Washington. Australia has had a formal working group on missile defence with the United States since 2014. Senator Payne said that "it's fair to say that has added some issues to its agenda in recent times".

She said that in announcing Aegis for the future frigates, "we've made a clear statement about the sort of capability that we want to have".

Asked whether it all added up Australia doing more on missile defence, she said: "I think that would be a fair statement, yes."

So what good is a ship-based missile defence capability if it can't defend Australia from Darwin to Hobart? The first object, Dr Davies explained, is to defend itself and other allied ships or land forces in a theatre of war.

On either side of HMAS Hobart's upright shish kebab are two bubbles that house the satellite communications including an advanced ability to draw on nearby allied ships' and planes' own sensors. It means for instance that a ship can watch a threat through another ships eyes in real time and then shoot it down, still using those external eyes.

The nine future frigates plus HMAS Hobart and its two sister destroyers - which will be commissioned over the next couple of years - can work as a team. Because US and Japanese destroyers also use Aegis, all three countries' navies can operate as a network to provide some regional defence against rogue missiles.

Intercontinental ballistic missiles - the type North Korea would need to reach Australia - are very hard to shoot down because they fly well outside the atmosphere and come down at terrific speeds. The US has shot down such long-range missiles in tests but only using much bigger ground-based interceptor missiles.

It is possible that a ship-based interceptor missile could shoot down an ICBM early in its flight before it has left the atmosphere, but as Dr Davies said, this has never been demonstrated and it would require the ships to sit very close to the launch point, meaning in the Sea of Japan in the case of defending against North Korea.

Australia would also need a significant armoury upgrade on both the Hobart-class destroyers and the new frigates.

HMAS Hobart carries SM-2 missiles made by the US firm Raytheon though it is almost certain that by the middle of next decade they will have the longer-range SM-6 missiles. Both of these can be used for shorter range missile defence.

But to chase down anything at a longer range, Australia would need the even bigger SM-3, the latest version of which can travel 2500 kilometres at more than 18,000km/h.

Along with its allies, Australia can start to build what the Chief of Navy Tim Barrett last week called "layered" defence - a regional network protecting against a variety of threats at different ranges.

Dr Davies concluded that "the take home message is that Australia is heading down the road of acquiring a formidable ability to protect its fleet at sea from a range of credible air threats, as well as the ability to work with partners to tackle long-range missiles at their source".