USS Helena (CL-50) was a Brooklyn-class light cruiser built for the United States Navy in the late 1930s, the ninth and final member of the class. The Brooklyns were the first modern light cruisers built by the US Navy under the limitations of the London Naval Treaty, and they were intended to counter the Japanese Mogami class; as such, they carried a battery of fifteen 6-inch (150 mm) guns, the same gun armament carried by the Mogamis. Helena and her sister St. Louis were built to a slightly modified design with a unit system of machinery and an improved anti-aircraft battery. Completed in late 1939, Helena spent the first two years of her career in peacetime training that accelerated as tensions between the United States and Japan increased through 1941. She was torpedoed at the attack