Which new weapon was used against Japan during World War II?

The atomic bomb represents a significant advancement in warfare technology during World War II. Developed as part of the Manhattan Project, the atomic bomb was distinct because it relied on nuclear fission to unleash a tremendous amount of energy in a single explosive event. In 1945, the United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki, leading to widespread devastation and contributing to Japan's eventual surrender.

This choice highlights the unprecedented destructive capability of nuclear weapons and their profound impact on the course of the war, as well as on international relations in the subsequent Cold War era. The atomic bomb not only marked a turning point in military strategies but also raised ethical and moral questions about the use of such weapons in warfare.

The other options, while representing different types of weapons used in various contexts, do not capture the unique and historic nature of the atomic bomb specifically used against Japan during World War II.