The Australian warship HMAS Sydney II is shown In this undated photo released by the Finding Sydney Foundation. A remote-controlled submarine delving 1 1/2 miles below the sea surface off Australia has revealed fresh clues to a ferocious World War II battle in which both the Sydney and a German ship sank, but many questions remain.

A lifeboat cradle of the Australian warship HMAS Sydney II is shown in this photo taken Thursday off the Western Australian coast. All the cradles where the lifeboats once hung were empty, but no survivors were ever found..

Canberra, Australia ? A remote-controlled submarine scouring the shipwrecked remains of an Australian warship has revealed new clues to a World War II battle that cost more than 700 lives. But the mystery persists: What caused Australia’s worst maritime tragedy?

Did a well-aimed German torpedo sink the pride of the Australian navy? Or was it a catastrophic explosion in the ship’s ammunition storage area that ensured that none of its 645 crew would survive?

Part of the puzzle was solved last month when a sonar search led by American shipwreck hunter David Mearns found the wrecks of battle cruiser HMAS Sydney and, nearby, Germany’s converted freighter HSK Kormoran.

Both vessels sank after the Nov. 19, 1941, battle, and previous attempts to find them proved fruitless.

Until now, the official record of the battle has been based on the accounts of German survivors who were captured as they drifted toward Australia in lifeboats.

The Sydney spotted the Kormoran as it was prowling for Allied merchant ships to sink, about 500 miles north of Perth. The Australian vessel moved to intercept the suspicious ship and demanded that it identify itself. The Kormoran hedged, raising flags that claimed it was a Dutch trader and sending misleading radio signals.

All the while, the Sydney was being drawn closer until it eventually lost the advantage of having longer-range weapons.

German survivors said the Kormoran eventually dropped the artifice, raised its German ensign and opened fire when the ships were within a mile of each other.

Crews engaged in a furious exchange of naval artillery, torpedo and machine-gun fire for about half an hour, though Australia’s official history says both ships were probably irreparably damaged in the first five minutes.

As they took to lifeboats and set off charges to scuttle their vessel around midnight, the Germans later described seeing the glow of fires aboard the Sydney as it drifted about 10 miles away.

Unanswered questions

For years, the Germans’ account of the battle was viewed with suspicion and left important questions unanswered. Among them: If the Australian ship was able to limp away – aflame, but afloat – why was there no sign lifeboats were launched?

The first photos transmitted from the wreck show the Sydney’s turrets still trained to its port side as they were when the Kormoran was in their sights.

All the cradles where the lifeboats once hung were empty.

Naval historian David Stevens said this does not mean the crew abandoned ship. The boats were tied to the upper decks and would likely have come loose as the ship sank.

“They’re the sort of stuff that gets really damaged when your upper deck is getting shot to pieces,” Stevens said.

As the Germans said, the top of a gun turret was blown overboard by gunfire. One photo shows a hole blasted by a direct hit between its twin guns.

The Sydney’s bridge section had clearly taken the brunt of the Kormoran’s heavy gun barrage and an 80-foot section of the bow had snapped off around where the Germans recalled a torpedo struck with devastating effect.

“All you can say so far is that the Germans’ descriptions are very accurate,” Stevens said after seeing the initial pictures and searchers’ reports.

Searchers have suspected since seeing high-resolution sonar images of the wreck last month that a torpedo weakened the hull and caused the bow to snap off, ultimately sinking the ship.

Another theory offered to explain the total loss of life is that the burning ship’s ammunition storage area erupted in a catastrophic explosion.

Conspiracy theories

The Sydney’s fate has captured Australian imaginations for generations, and the hulk’s discovery, announced by Prime Minister Kevin Rudd, led news bulletins and was splashed on front pages nationwide.

The sinking has fueled conspiracy theories – including one, denied by the Germans, that Australian survivors in the water were shot to death. And it has occasionally thrown up tantalizing clues.

Nearly three months after the battle, on Feb. 6, 1942, a decomposed body with a shrapnel head wound was found washed ashore in a lifeboat on Christmas Island, 1,100 miles north of the wreck.

The Australian navy found the unmarked grave in 2006 and have used DNA and dental records to try to identify the body. Although authorities are almost certain he was a Sydney sailor, they have so far excluded more than 500 of the crew without finding a match.

The government, which has spent $3.9 million on the search, has appointed a retired judge to hold an inquiry into the new evidence.

The loss of the Sydney stunned Australia and the government banned all media from reporting the news for 12 days as it scrambled to explain what happened.

Most of the 397-man German crew survived, plucked from the ocean by Allied warships and tankers or reaching the Australian coast in lifeboats.

The German captain, Theodora Detmers, maintained that, in accordance with the rules of war, his ship dropped its disguise and hoisted a German navy ensign before firing the first shot.

It was Detmers’ account of the battle, inscribed using a simple code in a German-English dictionary while he was a prisoner of war, that proved crucial to locating the wreck of the Sydney. He penciled tiny dots beneath letters, spelling out a few words on each page.

“We wouldn’t have found the wrecks as quickly as we did without these documents,” Mearns told Australian Broadcasting Corp. “They were very, very accurate.”

But some elements of the mystery are sure to endure.

“Did the Germans machine gun people in the water? Did they raise their flag before opening fire? We’re never going to answer those questions,” said Jeremy Green, chief maritime archaeologist at the Western Australian Museum.