For one thing, the country's unbelievably vast. Conquering the continent would require a huge amount of enemy troops and resources to suppress outbreaks of resistance from the local populace.

Wouldn't it be better for the Japanese to instead seize just one vital artery of the Australian war effort and cut it off?

Older Novocastrians know all about the concept of the Brisbane Line in WWII (1939-45). That's when our military authorities agreed to abandon the Top End of the nation, if necessary, and concentrate on protecting the industrially strong southern half.

That's where the Port of Newcastle and its surrounding area, including the Steelworks once run by BHP and the Williamtown RAAF fighter base, come into focus.

Although the Japanese military burned a lot of their records as WWII ended, it's long been suspected that there was a plan for them to ignore most of our coastline and, at some point, simply invade Newcastle instead. Once there, the enemy forces could dig in, creating a major toehold in the nation and not bother to move elsewhere. From their Lower Hunter base, the Japanese could have had a rather significant chokehold on Australia's war effort.

The enemy, who had earlier swamped the "invincible" British base at Singapore, could then have had a field day. At one stroke, they would have cut off supplies of BHP steel and the site of small arms manufacture, neutralised a key aircraft base and removed our much needed ship repair and shipbuilding facilities.

So, the possibility of Newcastle being invaded was very real. Why else was the Nelson Bay-Newcastle Road secretly mined? And why was Stockton Beach planted with scores, if not hundreds, of big, concrete tetrahedrons, or anti-tank traps, which haunt us to this day whenever big seas dislodge more beach sand?

Why else was a major force, thousands of American troops, suddenly based at Port Stephens, not Queensland, training beach commandos? And was the surprise shelling of Newcastle Harbour by a Japanese submarine on the night of June 8, 1942, intended as a scare, or to soften up civilians to flee, as some indeed did in panic, if only to New Lambton Heights?

All this is why this forgotten history needs to be remembered. And a new community project now underway called 'Fortress Newcastle' hopes to remedy that.

Involving a coalition of several interested heritage groups, it aims to discover more and promote the critical role our region played in saving Australia during WWII.

Bob Cook, of Heritage Hunter, says the latest bid to enhance public awareness of the district's overlooked wartime role is a new post on the Living Histories website at the University of Newcastle.

Here, it spells out how, at the start of WWII, Newcastle was the location of Australia's largest integrated steel making facility, surrounded by heavy industry, coal mines, a busy deep harbour for merchant ships plus a floating dock.

The task to defend these assets became known as Fortress Newcastle, the "largest military defence establishment in Australia's history", the website says.

The area stretched north to Port Stephens south to Tuggerah Lakes and west to Muswellbrook.

Largely forgotten now were anti-aircraft batteries at Tomago, Fern Bay, Mayfield and Stockton, plus army training camps at Largs, Rutherford, Greta, Gan Gan and Singleton.

The southern defence line though was humble Cold Tea Creek, south of Belmont, with its anti-tank ditch.

There were also RAAF radar early warning bases on the summit of Tomaree Headland at Port Stephens, at the top of Newcastle's King Edward Park, Ash Island, Catherine Hill Bay and 'Wipers' at Williamtown, plus a major seaplane base at Rathmines, on Lake Macquarie.

But the main deterrents to any attack were two six-inch (150mm) calibre guns at the coastal Fort Scratchley and Fort Wallace's two mighty 9.2inch (240mm) guns.

Sadly, however, these last two guns at Stockton couldn't depress low enough to fire on the enemy sub in June 1942.

A minefield was also laid across our port entrance and other big guns called the Park Battery were installed on high ground overlooking the ocean at the top of Shepherd's Hill (King Edward Park).

SPEAKING of World War II, remember the recent story about the hastily built fleet of American 'Liberty ships' some of which broke in half while on active service?

Once described as the ships that saved WWII, almost none of the fleet of almost 3000 still survive.

Little wonder, as these crucial supply ships were built only with a five-year lifespan in mind.

The story revived memories for former Newcastle mariner Andy Traill. He said that when he first went away to sea in 1967 there were still a few such ships around, but not many.

"When I then started to pilot ships up and down the Great Barrier Reef in 1990, I recall flying into Lockhart River on the way to Horn Island in the Torres Strait," he said.

The airstrip was quite big for such a relatively isolated spot, and he soon discovered why.

"According to my colleagues, the area (also known as Iron Range) was the site of a rather large stores depot during WWII and they recalled some of the older pilots relating stories of some 20 Liberty ships at anchor in the area, discharging supplies for the Battle of the Coral Sea," Traill said.

"Apparently the area was far enough south that if the Japanese took Port Moresby, then it was still too far south for the Japanese aircraft to make the bombing journey.

"Probably a pity that these are all anecdotal stories, maybe it is written down somewhere," he said.

Meanwhile, what was the likely cause of the many of these Liberty supply ships suffering brittle fractures in their decks and hulls and even sinking?

Charlestown reader John McLennan may have part, at least, of the answer to the mystery.

In WWII, German U-boats were sinking cargo ships faster than they could be replaced using existing construction techniques. Therefore, US building methods were revolutionised to construct cargo ships much faster, in weeks, rather than months.

McLennan said he was seconded by the Australian Department of Supply to the National Physical Laboratory at Teddington, England, in 1952-53.

Here, metallurgists investigated why some Liberty ships broke in half during the passage from the US to Liverpool, England, in WWII.

He said it turned out that the US mild steel being used in construction was low in manganese, which resulted in a coarse microstructure that was brittle at low temperatures.

To avoid German U-boats, Liberty ships were taking a northerly Atlantic route in winter when cracks could then appear at high stress points, causing hulls to break in half.

McLennan said a ship constructed by the older method of riveting plates together (instead of the new, faster welding process) had a better chance as it meant only losing a plate as the rivets readjusted to the stresses.

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