On May 7, 1915, one hundred and eleven years ago yesterday, the British ocean liner Lusitania was torpedoed without warning by a German submarine off the south coast of Ireland. Within 20 minutes, the vessel sank into the Celtic Sea. Of 1,959 passengers and crew, 1,198 people drowned, including 128 Americans, such as Alfred Gwynne Vanderbilt, one of the richest men in the United States at the time and member of the storied Vanderbilt clan.

Although tragic, the sinking of the Lusitania was by no means an isolated event. On August 19, 1915, the Germans targeted and torpedoed the SS Arabic, a White Star ocean liner en route to New York from Ireland. 44 people died when the ship sank. A few months later, in November, the HMHS Britannic suffered a catastrophe when the ship hit a mine left by the German Navy near the Greek island of Kea, costing 30 lives. And in 1916, a German U-boat fired upon the SS Sussex, a French passenger ferry, in the English Channel, killing over 50. All in all, from 1914-1918, over 6,000 Allied and neutral ships were sunk by U-boats. The German Navy specifically targeted close to 50 foreign passenger ships as a part of its military campaign, using direct ambushes and underwater mines to sink enemy vessels.

And yet it is the Lusitania that became the rallying cry for Americans as the country entered World War I and still most remembered all these years later.

Why?

It all depends on who you ask.

When World War I erupted in 1914, President Woodrow Wilson pledged neutrality for the United States. Britain, however, was firmly entrenched in the conflict. As one of America’s closest trading partners, tension soon arose between the United States and Germany over the latter’s attempted “quarantine” of the British Isles by announcing unrestricted submarine warfare in the waters around Britain. Ignoring previous wartime engagement “cruiser laws,” which stated merchant ships were to be warned by warships and their passengers and crew allowed to abandon ship before they were sunk, the German government decreed that “every enemy merchant vessel encountered in this zone will be destroyed, nor will it always be possible to avert the danger thereby threatened to the crew and passengers. Neutral vessels also will run a risk in the War Zone.”

So, when the Lusitania entered the waters in May 1915, both Britain and the United States believed it should be a protected vessel.

The Germans, naturally, thought otherwise. In their minds, they’d already released a warning. Any blood shed was not on their hands but on their enemy’s. As such, after the sinking, Germany refused to issue an apology for their actions, despite the staggering number of innocent lives lost, further solidifying their “villain” status within the United States and adding to the Lusitania‘s harrowing legacy.

Lore around the ship further grew when it was discovered the ship’s cargo wasn’t an innocent as the British originally claimed it to be.

The Lusitania wasn’t just transporting people. It was also carrying about 173 tons of war munitions for Britain, including 4.2 million rounds of rifle ammunition, almost 5,000 shrapnel-filled artillery shell casings, and 3,240 brass percussion fuses.

Britain had been playing its own game of subterfuge, transporting war materials under the guise of a neutral ship.

Another reason for the staying power of the Lusitania‘s legacy is the mystery held in the moments of its sinking.

Many survivors from the Lusitania reported a second, larger explosion taking place either immediately or a few seconds after the first, initial hit. This explosion has been used to explain the speed of Lusitania’s sinking, with the behemoth disappearing beneath the waves less than twenty minutes after the attack.

The only problem? No one knows exactly what the second explosion actually was.

At the time, official inquiries attributed the blast to a second torpedo attack from the U-boat, as was recalled by multiple witnesses. However, testimony and radio communications from U-20 makes clear that only one torpedo was fired towards the ship. U-boat captain Schwieger even wrote in his war diary that firing a second torpedo was impossible due to the crowd of frenzied passengers who dived into the ocean in panic.

Was there a second U-boat present, then? One whose involvement was carefully covered up? And, if so, why?

Others theorize the second explosion may have come from the ship’s secret military cargo. However, the small arms ammunition were known to be non-explosive in bulk, and an inquiry at the time of the sinking found that there were no other explosives on board.

But not everyone believes this. Some, like author Steven L. Danver, allege that Lusitania was also secretly carrying a large quantity of nitrocellulose (gun cotton). Another theory suggests that the 90 tons of butter and lard listed on the customs form may have been something else. Additional speculation centered on a consignment of furs, sent from Dupont de Nemours, a company that also manufactured explosives. Still others have suggested that the shells were in fact live, not empty as the British government claimed.

But perhaps the biggest controversy surrounding the Lusitania is the claim the ship was deliberately placed in danger by the British authorities, so as to entice a U-boat attack and thereby drag the US into the war. This theory stems from a letter written by Winston Churchill to Walter Runciman, the President of the Board of Trade, in early February of 1915, where he stresses it’s “most important to attract neutral shipping to our shores, in the hope especially of embroiling the United States with Germany.” Theorists also point out several questionable decisions made by authorities before the ship’s sinking, such as the awareness of a German submarine in the path of Lusitania, but the decision not to divert the ship to a safer route; the refusal to provide the ship a destroyer escort, standard practice during war time; and the commandment to reduce speed in the war zone despite danger.

If this, indeed, was the plan of the British government, they got their wish…but not until two years later. The United States officially entered World War I on April 6, 1917.

Whether for all these reasons or others not yet explored, the Lusitania continues to loom large in the public’s imagination, the tragedy, as well as her mysteries and secrets, still beckoning from her watery grave.