I-8 hit rough seas in the South Atlantic off the Cape of Good Hope, which delayed her arrival in Singapore. She radioed her position to Germany, but the message was intercepted by the Allies, prompting an attack by anti-submarine aircraft, which failed. I-8 arrived in Singapore on 5 December, and finally returned to Kure, Japan on 21 December, after a voyage of 30,000 nautical miles (56,000 km).