And it links to a larger effort to map key sites along the famous trail before they are lost to erosion, jungle creep and damage from clumsy trekkers.

“We went along it (the Jap Road) with a GPS and were able to map part of it,” says Matthew Kelly, senior archaeologist with Extent Heritage, whose team undertook the study for the PNG government.

The muddy, narrow mountainous Kokoda Track, fought over in horrible conditions between July and November 1942, was passable only to men on foot — and at times even then with great difficulty.

But the ‘Jap Road’ which runs parallel to the famous track is some metres wide, with banked sides, and investigators — who have crosschecked with old battalion memoirs and Australian War Memorial archives — believe it was intended for use by horses bringing supplies.

The invading force brought thousands of horses to PNG; given that they already outgunned the Australians with artillery and heavy machine guns, but had their initial successes eroded by their overextended supply lines, had they managed to pull even more equipment up the track the battle could have altered considerably.

“It would have changed things,” says Sydney-based Kelly. “This one would have been unknown to Australian intelligence. They could strafe the Kokoda Track but they couldn’t see the Japanese moving back and forth along this one.

“And the suspicion they might have been using horses to haul more supplies would not have been anticipated because the Australians had tried to use horse transport and failed.”

Kelly does not believe the road would have ultimately changed the outcome of the campaign, once the Japanese were forced to retreat; but had it been further developed it would have enabled the enemy to put up an even more vigorous defence which would have cost hundreds of Australian casualties.

The next step is to establish how far north and south the road extends. So far Kelly’s team have mapped just 4km in the vicinity of the lost battlefield.

“The proof of the pudding will be in further surveying,” says Kelly.

“If they didn’t build a track all the way from Kokoda all way through to PORT Moresby it looks as though they were looking at the possibility of doing so and that they may have been able to build part of it before they were forced to retreat.”

Etoa is near Eora Creek, site of one of the most significant battles along the track, where the retreating Japanese seemed set to hold the advancing Australians — until the Aussies broke through with well-recorded feats of courage.

Kelly believes there are many more stories waiting to be unearthed along Kokoda — from fallen soldiers’ remains to crashed planes, and even the remains of a massive defensive wall built by the Japanese and mentioned by diggers but never located.

Meanwhile PNG’s National Museum has appointed Australian historian Dr Andy Connelly as its new military heritage adviser as it seeks to discover and tell those stories.

Connelly was part of an expedition last year to locate and map more than 200 previously unrecorded sites of interest along the track, ranging from emplacements and ambush sites to weapons pits, where hoards of armaments can still be found.