The ocean was black and endless and filled with nothing. There was just an ever-increasing heaviness. A feeling of weight and pressure.

They followed a line of coloured lights — glow sticks tied at intervals to a rope known as a shot line — until they reached the bottom.

Out of the gloom came a line of pink. Then green. Then blue. Disco sticks shaken and cracked to give off a fluorescent glow, a path of breadcrumbs leading out of the forest.

Slowly — very slowly — they sank to a depth of 178m. It was a record breaking dive. A difficult — and very dangerous — attempt at proving something they were quite sure of.

Whatever ship was down there, it wasn’t the Centaur.

At 178m, only the weakest hint of daylight made its way to the bottom. To expert wreck diver Trevor Jackson and his dive buddy, Dr Simon Mitchell, it was a little like standing in your backyard in the middle of the night. You can make out the shape of your house, the car, the clothes hanging on the line. But not much else.

At such a depth, even breathing was difficult. Movements were slow but their effects exaggerated. The slightest kick of a fin propelled them forward. But even the smallest effort had them out of breath. Down here, everything was dangerous. They risked lapsing into unconsciousness if they lingered too long.

Jackson came across the weight at the end of their shot line. A large, disused tank. They searched the darkness for the outline of a ship, a great hulking shape. But there was only sand.

The pressure of 178m of water was playing havoc with their equipment. Their video equipment malfunctioned. Their lights blew out — all but a tiny penlight Jackson had brought with him. A cheap thing he’d thought would be the first to go.

He thought they’d missed the wreck entirely. But then they noticed a fire extinguisher sitting on the ocean floor. Had they taken the brass plaque attached to its side, it would have proved things one way or another.

But they were possibly dealing with a war grave. They’d vowed not to disturb it.

Then, to Jackson’s left, he noticed the fish.

In an area where nothing but sand carpeted the ocean floor, there was only one reason for the sudden appearance of a multitude of fish.

A wreck will eventually form its own eco system. Weeds and coral drift, collect and grow. Tiny sea creatures follow. Eventually it will teem with tiny fish. Then larger fish.

Jackson and Mitchell followed the fish to a large shape that didn’t even seem to be a boat at first. It seemed alive. An ever moving shape, teeming with life. Thousands of fish covered every inch of its coral-clad surface.

But, underneath it all, was a boat. A small boat. At around 55m, it was less than half the length of the Centaur.

It was 2002 — nearly 60 years since she’d gone down — but thanks to Jackson and Mitchell’s record breaking dive, the search for the Centaur was on again.

IN THE waters off Brisbane, not far from the electric flash of the Cape Moreton Lighthouse, a hospital ship hugged the Queensland coast.

She was on her way from Sydney to Port Moresby, where they planned to collect soldiers injured in battles at Gona and Buna.

On board were 332 people. No soldiers. Just a crew of 75 merchant seamen and a couple of hundred medical staff, nurses, the 2/12th Field Ambulance Unit and army ambulance drivers. Many had been travelling together for some time. They’d formed the kind of close bonds that come with facing danger and sharing tragedy.

They’d left Sydney on May 12. The following night put them off the coast of Queensland, the ship’s bright lights casting a glow across an inky ocean.

A hospital ship had no need to hide. They carried no weapons, no troops. They were no threat to anyone and should have been off limits to the enemy. Painted on her sides were large red crosses. The number 47 decorated the Centaur’s bow — an identifying mark signifying her registration with the International Red Cross.

And it was not a night for hiding. A full moon blazed in the sky. The stars lit their way.

Private Bill Burrett joined the army at the age of 18. He’d left his job as a shop assistant at a Coles store in Sydney to serve his country. Two years later, after returning from the Middle East, he transferred to the Centaur.

“You’re in dangerous waters now,” his brother told him.

“I’m not worried,” Bill told him. After all, he’d be on a hospital ship. They were hardly a target.

ELLEN Savage was the daughter of a Russian-born tailor and his country New South Wales wife. She grew up in Quirindi, a tiny town south of Tamworth.

She was in her early 20s when she graduated from nursing but went on to study obstetrics.

In 1941, with World War II well underway, Ellen signed up with the Australian Army Nursing Service. After a stint at a hospital in Sydney, the 168cm blue-eyed, fair headed country girl boarded a hospital ship named Oranje and headed for the Middle East.

She was quickly promoted, first making sister and then lieutenant.

In May, 1943, like many of her fellow Oranje medical personnel, Ellen transferred from Oranje to HAS Centaur.

She was one of 12 nursing sisters set to travel to New Guinea. Ellen’s cabin was alongside Evelyn King’s. The two were best friends and excited about setting off on a new adventure.

They’d talked about what would happen if anything ever went wrong. Ellen was a strong swimmer. Evelyn couldn’t swim at all.

Ellen had told her not to worry.

“I’ll crocodile you,” she’d said. In other words, should they end up in the water, Ellen would fling her friend over her shoulders and help her stay afloat.

On the second night of their trip to New Guinea, the sisters got together to throw a party for Matron Ann Jewell.

The girls had smuggled a cake on board and the ship’s chef had iced it. “Happy Birthday from the Centaur” was written in pink icing across its top but nobody dared to add candles. Some of the men thought about asking her how old she was but decided it wasn’t worth the risk.

They watched and smiled as the women sang to her. They’d decorated the table and a special celebratory dinner menu had been served.

The men were celebrating too. The ship’s purser had just become a father. He’d have a new baby at home when they returned.

They went to bed with bellies full of cake and smiles on their lips.

Then, at 4am, as the Cape Moreton lighthouse blinked in the distance, the Centaur was suddenly, violently ripped apart by a single torpedo.

Most of those aboard were sound asleep when the torpedo slammed into her side, 2m below the waterline. A roaring fire raced through the lower decks, trapping many in their beds. Oil poured into the water as the vessel cracked and split. People ran for their lives. Many were already dead.

Ellen jumped out of bed. Her cabin had rocked and trembled with the force of the explosion. She looked out her porthole to the orange glare of fire. She found Evelyn and they raced for the main companionway. They found it ablaze. An impenetrable wall of heat and flames. They had to find another way.

They ran for another stairwell. This one was clear. The women surfaced on the Centaur’s top deck to a roaring fire. The bridge was alight. Ellen could feel the boat sinking under her feet.

She grabbed hold of her lifebelt and looked at her friend. They would jump together.

Around them, people helped each other with an incredible sense of calm.

“That’s right girlies,” a cheeky voice said as Ellen and Evelyn approached the edge. “Jump for it!”

They jumped.

Evelyn hit timber on the way down with enough force to kill her. Ellen landed in the water and was pulled down with the suction of the sinking boat. She held what air she could in her lungs as pieces of debris struck her all over her body. Something hit her in the head so hard she almost lost consciousness.

She fought the water, fought the debris. She felt rope tangle around her legs and she fought against that too. Which way was up? She was dizzy from panic, dizzy from a lack of oxygen and from the knock to her head.

Then, suddenly, she broke the surface. She gasped for air in the churning water. Next to her was a man. He was gasping too.

The Centaur was a burning husk, a glowing coal against a black sky. It was going under — and fast.

Oil spread across the water in a thick slick, burning their eyes. It was only a matter of time before it caught alight and burnt them all.

Ellen put her head down and swam.

SHIPWRIGHT Ronald Bull made it to the top deck before the Centaur sank. He wrestled with the life raft on the starboard side, trying to free it as the ship broke apart around him.

Spars — crossbeams from the mast — fell from the sky, landing with enormous crashes on the splintering deck.

“Look out for the spars!” an orderly yelled as Bull dodged some falling rigging.

A moment after shouting the warning, the orderly was himself killed by a falling spar.

Ronald freed the raft and fell into the ocean. The water sucked him down. Metre after metre, he was sucked into the ocean. He thought his lungs might burst.

When he surfaced, his leg was caught in the casing of the raft. He was missing his underpants and his teeth had been knocked out.

People were trying to clamber into the raft as he worked to untangle his leg. Ronald could swim. He left them to it, making his way to a hatch cover that would keep him afloat for a while.

CAPTAIN Richard Salt was a 67-year-old Sydney man and a Torres Strait pilot who’d already spent 50 years at sea. Survivors would describe him as the toughest man to make it out alive.

Flames had trapped him at every turn. If he stayed where he was, he’d be burnt alive.

He grabbed a blanket and dragged it over his body. Next, a bucket of water. He upended it over his head, soaking every inch of the fabric. He took a breath and faced the wall of flames. And ran.

He hit the water and fought his way to the surface as the ship tried to drag him down.

He came up with terrible burns to his face and hands. Everyone who saw them thought he must have been in terrible pain. But he never even let out a whimper.

SURVIVORS surfaced, clinging to rubber rafts and hatch covers. Two men came up together, grabbing for barrels that had floated to the surface. One screamed and jerked back under. The other kicked away, staring in fear at the place where his mate had been. There were sharks in the water.

Ellen found herself holding onto a section of the deckhouse. She helped a young cabin boy, 15-year-old Robert Westwood, onto the piece of wreckage.

They formed a raft with lifeboats and pieces of large, floating debris. They grabbed torn wires and tied everything together.

Someone fished out a first aid kit and they used it to treat the wounded. A man gave a freezing Ellen his greatcoat. It undoubtedly saved her life. She shared it with the cabin boy, saving his life too. Most of the survivors were naked, or barely clothed. They all huddled together to keep warm. It rained on them, miserably, throughout the night.

Then, they heard a noise. The humming of an engine. At first they thought it was a plane.

And then, a call came through the night.

“Coo-ee!” someone shouted. A small green light lit broke out against the dark sky.

“Don’t answer!” a man whispered urgently. He’d been in Rabaul, New Guinea, and had heard the call before.

“They tried that in Rabaul. They’re Japanese. Remember, sailors never say `Coo-ee’, they say `Ahoy’.

They held their breaths, expecting the chatter of machine gun fire to finish what the torpedo had begun.

But the dark kept them hidden and soon they were alone once more.

Ellen kept busy treating the wounded. Massaging burnt limbs.

She had grabbed her rosary beads as she ran from her room. She’d held onto them through everything. She held them as she led them in prayer. It kept them calm.

They gave her control of the food and she measured it out to last them four days.

A meal was a lick of meat extract, a milk tablet, two prunes and a sip of water.

The man placed bets on the hour of their rescue. They sang songs and held each other close.

They shouted with joy when a plane approached. They lit a flare. But it flew in the other direction.

Things were quieter after that. A man died from his wounds and they buried him at sea.

Sharks circled. They counted seven at one point. One lunged at them, sliding right up into the raft. They fought it off with a plank of wood.

The hours wore on. Four ships passed in the different. More planes flew by. But nobody saw them.

ON THE morning of May 15, an American destroyer left Brisbane to escort a New Zealand freighter on its voyage home.

It was 2pm when a lookout on board the destroyer spotted an odd shape in the water.

A moment later, a Royal Australian Air Force plane on submarine watch found survivors grouped together on makeshift rafts, floating with the current.

The plane dived at the survivors. Help was coming.

The American destroyer was upon them in minutes. Sailors lined the deck, rifles trained at the water to shoot at the circling sharks.

Others jumped into the water, swimming fearlessly towards the injured.

They were saved.

OF THE 332 medical personnel and crew who’d boarded the Centaur when she left Sydney, only 64 survived. Among the dead was Bill Burrett, who’d told his brother not to worry.

Several others would later die from burns and shrapnel wounds. Second officer Gordon Rippon was the most senior crew member to make it out alive and only one doctor lived through the attack. Three brothers from Holroyd, New South Wales, had been on board. All three were killed.

“PLEASE be kind to me … and don’t ask me too much,” Ellen said from her hospital bed days later.

She’d barely slept. Nightmares ripped through her when she closed her eyes. She’d cried for her friends. For Evelyn, who’d jumped with her and died, while Ellen had surfaced.

Twelve nursing sisters had been on board the Centaur. Only Ellen had made it out alive. She’d hidden her own injuries as she’d treated others.

In hospital, she was treated for severe bruising, a broken noise, burst ear drums, a broken palate and fractured ribs. She’d spent 36 hours in the water waiting for rescue.

Now, she lay in a hospital room, where newspaper men stood with pen and paper to talk to the woman everyone had labelled a hero.

“I’m not important,” she told them.

“After all, those other girls who were with me …”

She trailed off.

But she was important.

In 1944, Ellen became the second Australian woman to be awarded the George Medal, given to her for “conspicuous service and high courage”.

* The AHS Centaur was discovered in December 2009 after a multimillion-dollar government investment equipped search teams with a side — scan sonar system and a remotely operated vehicle. The stricken ship was in 2059m of water 30 nautical miles east of Moreton Island.

* The torpedo attack of an Australian hospital ship was met with widespread international condemnation. But the Japanese maintained they had mistaken the clearly marked Centaur for another ship.