She measured just under 171 feet (52 m) long and displaced nearly 400 metric tons (390 long tons) on the surface and just over 550 metric tons (540 long tons) when submerged. At the outbreak of the First World War in August 1914, Curie was assigned to duty in the Mediterranean. In mid-December, Curie's commander conceived a plan to infiltrate the Austro-Hungarian Navy's main base at Pola, but during the 20 December attempt, the vessel became ensnared in harbor defenses.