Robot Probes Mystery of Lusitania’s Sinking : World War I: Robot examines wreckage of passenger ship sunk by Germans in 1915, dooming nearly 1,200.

The commander of the German U-boat couldn’t believe his luck. Just when he thought the massive steamer was going to escape along the south coast of Ireland, it turned sharply toward him.

The British liner RMS Lusitania, on her way from New York to Liverpool, England, with 1,959 passengers aboard, couldn’t have run a better course if it voluntarily intended to come into torpedo range, Walther Schwieger told a friend. From 750 yards, he fired a single torpedo. It was 2:10 p.m. on May 7, 1915.

Eighteen minutes later, the ship hit the bottom of the Celtic Sea, off Ireland. Only 764 people were saved. The 1,195 victims included 94 children and infants.

The Lusitania has remained shrouded in mystery and controversy ever since.

Why were there two explosions rather than one? Why did she sink so fast? Was the Lusitania, as Germany claimed, secretly transporting munitions that ignited on impact?

In hopes of answering some of these questions, a team of scientists sponsored by the National Geographic Society explored the shattered vessel with three remote-controlled underwater vehicles for nearly two weeks last summer.

Passengers boarding the Lusitania at New York’s Pier 54 on May 1, 1915, knew of Germany’s threat to sink ships in the war zone around the British Isles. The two nations had been fighting for nine months. Some travelers may even have seen the ominous notice published in newspapers that morning, advising them of the risk. But few imagined that a civilized nation would attack an unarmed passenger steamer without warning.

German authorities, however, now saw the great liner as a threat. They accused the British government of using the Lusitania to carry munitions and other contraband across the Atlantic.

At 2:10 p.m. on May 7, Leslie Morton, an 18-year-old lookout on the Lusitania’s bow, spotted thin lines of foam racing toward the ship. “Torpedoes coming on the starboard side!” he shouted through a megaphone, thinking the bubbles came from two projectiles. The impact sounded like a “million-ton hammer hitting a steam boiler a hundred feet high,” one passenger said. A second, more powerful explosion followed, sending a geyser of water, coal and debris high above the deck.

Listing immediately to starboard, the liner began to sink rapidly at the bow, propellers rising to the surface as passengers tumbled down her slanted decks. Lifeboats on the port side were hanging too far inboard to be readily launched, those on the starboard side too far out to be easily boarded. Several overfilled boats spilled occupants into the sea.

The huge vessel disappeared under the waves, leaving behind a churning jumble of swimmers, corpses, deck chairs, oars and a large mass of wreckage. Looking back upon the scene from his submarine, apparently even Schwieger was appalled. He later called it the most horrible sight he had ever seen.

Americans were outraged by the attack, which claimed the lives of 123 of their fellow citizens. Newspapers called the torpedoing “deliberate murder” and a “foul deed.” Politicians, including former President Theodore Roosevelt, demanded reprisals against Germany.

Within days of the sinking, German sympathizers in New York came up with a conspiracy theory: The British Admiralty, they said, had deliberately exposed Lusitania to harm, hoping she would be attacked and thus draw the United States into the war.

Perhaps the biggest puzzle of all was why the liner sank so fast. Newspapers at the time speculated that the torpedo had struck war materiel in a cargo hold, causing a mighty internal explosion--the secondary blast reported by survivors. Divers later reported a huge hole in the port side of the bow opposite where munitions would have been stored.

Hoping to settle the issue once and for all, National Geographic sent its robot vehicle, Jason, from the Woods Hole Oceanographic Institution in Massachusetts, down to photograph the damage. But when its cameras swept across the hold, researchers got a big surprise: There was no hole, no sign of explosion.

She looked more like a junkyard than a luxury liner when first photographed last July. Plunging bow first into 295 feet of water, the 785-foot-long ship slammed into the bottom while her stern was still at the surface. The force of the impact crumpled the stem of her bow and cracked open her hull amidships. After she crashed down on her starboard side, her decks collapsed, spilling debris onto the sea floor.

The liner’s giant funnels have long since turned to rust, her lifeboats have rotted away, and human remains have been consumed by sea creatures.

Seeing the name for the first time was like reading a tombstone: Here lies the LUSITANIA. An eerie marine growth covers her steel hull, and her superstructure has turned into ghostly wreckage.

Questions about her cargo have haunted the Lusitania since the day the ship went down. The Germans have always claimed she was carrying illegal munitions--which, in fact, she was. The manifest for her last voyage reads like a contraband shopping list.

But as the National Geographic investigation suggested, such war materiel did not cause the secondary blast that sent the Lusitania to the bottom. So what did?

A more likely possibility was a coal-dust explosion. The German torpedo struck the liner’s starboard side about 10 feet below the waterline, rupturing one of the long coal bunkers that stretched along both sides. If that bunker, mostly empty by the end of the voyage, contained a large amount of volatile coal dust, the torpedo might have ignited it.

Though relations among nations have healed in the years since, the horror and fascination of the Lusitania have never diminished. Exploration of her was like a somber return to the scene of a crime. With high-technology tools researchers searched for the “smoking gun” that might solve her riddles. But the truth about the sinking of the Lusitania remains as murky as the dark Celtic Sea.