Battle of Savo Island. The Battle of Savo Island was the first major naval battle in the Guadalcanal campaign and took place on August 9, 1942. U.S. Marines landed on Guadalcanal in the two days prior, and were occupying Henderson Field, while imperial Japanese forces conducted a surprise attack on the Allied naval forces in the area. The Imperial Japanese Navy undertook a night surface attack on the ships screening the Allied landing force. The battle has come to be identified as the worst defe