As the Japanese Eighth Fleet's Admiral Mikawa raced south down the Slot, U.S. Admiral Turner's amphibious force lay off the beachheads building up ashore as fast as they could. Responsibility for protecting Turner's transports lay with Admiral Crutchley and his Australian and American cruiser and destroyer force. The threat in general came from the north. Right at the northern end of what was to become Ironbottom Sound--between Guadalcanal and Tulagi--lay a small island called Savo. Savo was about to put its name on the worst defeat the U.S. Navy suffered in 130 years.
Geography prompted Crutchley to divide his force. Determined to make use of Savo to help block off the sound, he placed part of his ships (Northern Force, heavy cruisers Vincennes, Astoria, and Quincy, screened by destroyers Helm and Wilson) on one side of it, and a smaller one (Southern Force, heavy cruiser Chicago together with Australian Canberra, screened by destroyers Patterson and Bagley) on the other. Two more destroyers (Ralph Talbot and Blue) were pushed out beyond Savo to act as radar guard and ASW patrol. A third part (Eastern Force, light cruiser San Juan and Australian Hobart) was assigned to provide close-in protection to the transport area itself.