On August 7, 1942, U.S. Marines landed on the islands of Guadalcanal and Tulagi in the Solomons, putting the Japanese on the strategic defensive for the first time in the war. Vice Admiral Gunichi Mikawa, commander of the newly formed Eighth Fleet at Rabaul, reacted swiftly. Gathering five heavy cruisers, two light cruisers, and a destroyer, he sailed south and attacked the Allied naval force off the coast on the night of August 8–9. Mikawa's quick response resulted in the Battle of Savo Island, in which four Allied heavy cruisers were sunk with no Japanese ships lost. This was the worst defeat ever suffered by the U.S. Navy while at sea, only mitigated by the failure of the Japanese to attack the vulnerable American transports.