Final answer:
The RMS Lusitania was the British luxury liner sunk by a German U-boat in 1915, leading to the loss of over 1,200 lives, including 128 Americans. The sinking affected international sentiment and contributed to the United States joining World War I. The correct answer to the question is the Lusitania.
Step-by-step explanation:
The British luxury liner that was sunk by a German U-boat during World War I was the RMS Lusitania. On May 7, 1915, as it was travelling from New York to Liverpool, the ship was struck by a torpedo fired from a German submarine off the coast of Ireland, which led to it sinking in just under 18 minutes. The sinking resulted in the loss of over 1,200 passengers, among them 128 American citizens. This act of warfare contributed to shifting public opinion and had significant political ramifications, including influencing the United States' eventual entry into World War I.
Despite the fact that the Lusitania was carrying a large number of civilian passengers, it was also clandestinely carrying war materials, which the Germans justified as a valid target for their unrestricted submarine warfare campaign. After the tragedy, the German navy pledged not to attack civilian ships without warning under the Sussex Pledge. However, the restrictions of this pledge negatively impacted the effectiveness of the German U-boat advantage.
Therefore, the correct option in response to the question is the Lusitania.