What ship was sunk by the Germans that killed 128 people in World War 1?

I think what you're asking about is the British passenger liner RMS Lusitania. More than 1500 people died when she was sunk by a single torpedo fired by the German submarine U-20, including 128 Americans. She went down on May 8, 1915, and the outrage over this apparently callous act almost brought the US into WWI at that time, but, instead things cooled off and it was almost two more years before the US got into the war. For more than fifty years the British kept secret the fact that the Lusitania was carrying explosive guncotton in her hold, for use in making British artillery shells, and also had in her cargo millions of rounds of rifle ammunition for the British Army. These items were contraband under the naval blockade the Germans had declared of the UK, and knowledge that the British had exposed the passengers to the risk of sailing on a ship carrying contraband munitions of war would have taken away much of the Propaganda value the British received from the sinking of the ship. Also, the ship had been built partially with money from the British government, and was liable to be taken over by the British government in time of war, for use as a troopship or an auxiliary cruiser. She was listed on the naval register as an auxiliary cruiser, and thus was not a mere passenger ship. The German submarine captain had no way of knowing whether the British government had or had not taken the ship, and for all he knew it might be full of thousands of Canadian troops coming to fight the Germans. So, while at the time it looked to most of the world as though the Germans were complete monsters for sinking the ship, there was a lot more to the story that did not come out until the 1960s.