Situated at the junction of three oceans in one of the most strategically important regions in the world, Australia has made a significant decision to bolster its maritime firepower. 

If you don't know your frigates from your AWDs and your OPVs (defence is an acronym-rich environment, after all), here's a crack at trying to explain what the federal government has decided to do.

What does the Royal Australian Navy currently have?

At the moment, the Royal Australian Navy (RAN) has 11 ships in its "surface combatant fleet" – in other words, the ships that can be sent into conflict separate to its submarine fleet.

There are three Hobart class air warfare destroyers (AWD) – HMAS Hobart, HMAS Brisbane and HMAS Sydney.

Navy's three destroyers will have upgrades made by the end of next year.(Supplied: Royal Australian Navy)

At almost 148 metres long and tipping the scales at 7,000 tonnes each, their general purpose is to bolster the Navy's ability to protect other ships, troops and any defence buildings and infrastructure near the coast from attack by aircraft and missiles.

There are also eight Anzac-class frigates – although they're starting to get a bit old. The first of the class, HMAS Anzac, was put into service 28 years ago and is being retired as of today.

That's not the extent of the RAN fleet, as there are also patrol boats, supply ships and the like, but it is what's currently in the water and able to be used in combat situations.

The plan released today is for an increase in "surface combatant fleet" from 11 to 26, labelled "tier one" and "tier two" ships.

The three destroyers are part of that "tier one", and will be upgraded by 2025 by being given more advanced weapons systems, like bigger missiles that can travel longer distances (such as the US-made Tomahawk).

The Commonwealth had planned to build nine new frigates, known as the Hunter class. But it never actually inked a deal for the construction, merely the design process.

Its new plan involves six Hunter frigates, which will start being built this year – and there's talk of speeding up that process and potentially building two at the same time.

The frigates will be a fraction under 150 metres long and weigh up to 10,000 tonnes, and are billed as "anti-submarine" ships – meaning they'll be armed with weapons that can attack underwater threats as well as from the surface.

Manufacturer BAE and the RAN say the Hunter class will be one of the most advanced anti-submarine warships in the world, when they start coming into service next decade.

There's also a plan to acquire new smaller "tier two" frigates – 11 of them in fact, with at least the first three to be built offshore.

Four potential models have been identified, to help the Navy in missions such as securing shipping routes and patrol Australia's northern reaches.

German manufacturer Thyssenkrupp describes its Meko A-200 model as the "workhorse of the sea", and is the new version of the model used in the Anzac class frigates.

Japanese manufacturer Mitsubishi Heavy Industries has signed a deal to supply its Mogami 30FFM frigate to the Indonesian Navy, while the South Korean Daegu Class FFX Batch II and III has also been suggested as an option for the RAN.

The fourth possible model is the Spanish designed ALFA3000 by Navantia – the same company that designed large parts of Australia's destroyers.

In addition to this, the RAN will work with the United States to get its hands on six 'Large Optionally Crewed Surface Vessels' (LOSVs) – which can be unmanned.

Are we talking about robot ships?

Potentially, yes.

The LOSVs won't need a crew – or, at the very least, they won't need a full contingent of sailors to be able to go about their work, and can be controlled from elsewhere.

That helps their range and allows them to carry more firepower, not weighed down by people.

The idea is believed to be something the head of the surface review, US Vice-Admiral William Hilarides, is particularly fond of, and mirrors plans by the US Navy.

Although even the Americans don't have any in service yet – they're looking to have them in the water by the end of this decade.

Given the history of delayed defence projects in this country, this could be an interesting one to watch.

What's on the scrap heap?

As well as cutting back the number of Hunter frigates, the number of Offshore Patrol Vessels (OPVs) which will be built has been halved.

The OPVs are among what Defence is calling "minor war vessels" – and don't meet the changing requirements of the Navy.

Their use will be focused on "civil maritime security operations" and "regional engagement" through the southwest Pacific and southeast Asia.

Fewer offshore patrol vessel will be built than previously planned.(Department of Defence)

Where will all these new ships be built?

The shipbuilding states of South Australia and Western Australia were awaiting this decision with considerable anticipation and anxiety.

The "tier one" ships will be built at the Osborne shipyards in Adelaide's north – which is also the future home of the AUKUS nuclear submarine construction.

While that's good news for the local economy, and seems to avert the often cited "valley of death" scenario – where one project winds down before another begins and jobs are lost – the South Australian Premier Peter Malinauskas is already warning finding the workforce will be tricky, noting it will need to double in the next 2.5 years alone.

The "tier two" ships will be built in the west, at the Henderson shipyards in Perth's south.

OPVs are already being built at Henderson, as are the Evolved Cape class patrol boats — of which 19 will be acquired (eight for the Navy and 11 for the Australian Border Force).