Final answer:
The Hunley submarine was developed during the American Civil War with the goal of breaching the Union naval blockade of South Carolina's port cities. This was a strategic effort by the Confederacy to counteract the Union's attempt to isolate the Southern states.
Step-by-step explanation:
The strategy behind the development of the Hunley submarine was (C). It was developed with the goal of breaking through the Union blockade surrounding the port cities of South Carolina. The Confederate States sought to counteract the Union's naval power and blockade, which was intended to isolate and starve the Southern states by preventing the import of goods and the export of cotton.
The Hunley represented an innovative attempt to challenge the Union's control over key ports and sea routes. However, despite its groundbreaking design and intention to carry out covert underwater attacks, the Hunley faced many challenges and was plagued with difficulties, leading to its sinking and the loss of its crew during its combat mission.