THEY were the last line of defence against an enemy sea invasion of the Hunter's coast during World War II.
After being buried for decades, dozens of triangular concrete tank traps along Stockton Beach have been exposed by recent heavy seas.
Although a familiar site on remote parts of the beach, the recently uncovered traps have surprised locals.
One example near the main swimming beach bears the date February 23, 1942.
The interlocking rows of tank traps, known as tetrahedrons, were laid between Port Stephens and Lake Macquarie during 1942.
"I can certainly remember them at Newcastle and Bar Beach; they were everywhere" Fort Scratchley Historical Society vice-president Carl Christie said.
The Hunter coast was considered the most likely invasion point for the Japanese.
It was feared they would quickly move to take out the the city's industrial heart, BHP steelworks, which was critical to the manufacture of weapons and ships.
Although thousands of the traps were removed following the war's end, many others remain in place.
Newcastle City Council director of infrastructure Frank Cordingley said the council was aware that a number of traps had been exposed.
"Our crews are in the process of erecting signage to alert visitors as a safety precaution," he said.
"Council expects the tank traps will be re-covered when future high seas or storms return sand to the beach."