The Imperial Japanese Navy, in response to Allied amphibious landings in the eastern Solomon Islands, mobilized a task force of seven cruisers and one destroyer under the command of Vice Admiral Gunichi Mikawa.

In a night action, Mikawa thoroughly surprised and routed the Allied force, sinking one Australian and three American cruisers, while suffering minimal damage in return.

This early withdrawal of the fleet left the Allied ground forces (primarily United States Marines), which had landed on Guadalcanal and nearby islands only two days before, in a precarious situation with limited supplies, equipment, and food to hold their beachhead.

[8] The battle was the first of five costly, large-scale sea and air-sea actions fought in conjunction with the ground campaign on Guadalcanal, as the Japanese sought to counter the American offensive in the southern Pacific.

If Japanese air and sea forces were allowed to establish forward operating bases in the eastern Solomons, they would be in a position to threaten the critical supply routes between the U.S. and Australia.

[10]: 14–15  On 7–8 August Japanese aircraft based at Rabaul attacked the Allied amphibious forces several times, setting fire to the U.S. transport ship George F. Elliott (which later sank) and heavily damaging the destroyer USS Jarvis.

Mikawa, commander of the newly formed Japanese Eighth Fleet headquartered at Rabaul, loaded 519 naval troops on two transports and sent them towards Guadalcanal on 7 August.

At 10:20 and 11:10, his ships were spotted by Royal Australian Air Force (RAAF) Lockheed Hudson reconnaissance aircraft based at Milne Bay in New Guinea.

[11]: 139–50 [g] U.S. official historian Samuel Morison wrote in his 1949 account that the RAAF Hudson's crew failed to report the sighting until after they had landed and even had tea.

Later research has discredited this version of events, and in 2014, the U.S. Navy's Naval History and Heritage Command acknowledged in a letter to the Hudson's radio operator, who had lobbied for decades to clear his crewmates' name, that Morison's criticisms were "unwarranted.

At that time, several surviving Japanese aircraft from the noon torpedo raid on Allied ships off the coast of Guadalcanal flew over the cruisers on the way back to Rabaul and gave them waves of encouragement.

Turner had requested that U.S. Admiral John S. McCain Sr., commander of Allied air forces for the South Pacific Area, conduct extra reconnaissance missions over The Slot in the afternoon of 8 August.

[10]: 32 In the evening, Turner called a conference on his flagship off Guadalcanal with Crutchley and Marine commander Major General Alexander A. Vandegrift to discuss the departure of Fletcher's carriers and the resulting withdrawal schedule for the transport ships.

Although several of the Allied ships heard and/or observed one or more of these floatplanes, starting at 23:45, none of them interpreted the presence of unknown aircraft in the area as an actionable threat, and no one reported the sightings to Crutchley or Turner.

[11]: 165–66  Mikawa's force approached in a single 3-kilometer (1.9 mi) column led by Chōkai, with Aoba, Kako, Kinugasa, Furutaka, Tenryū, Yūbari, and Yūnagi following.

[10]: 36  When Blue was less than 2 kilometers (1.2 mi) away from Mikawa's force, she reversed course, having reached the end of her patrol track, and steamed away, apparently oblivious to the long column of large Japanese ships sailing past her.

[1]: 105 [j] The crew of Chicago, observing the illumination of their ship by air-dropped flares and the sudden turn by Canberra in front of them, came alert and awakened Captain Bode.

[1]: 105–06 Meanwhile, Patterson engaged in a gunnery duel with the Japanese column, receiving a shell hit aft that caused moderate damage and killed 10 crew members.

[10]: 41–44 [l] Between 02:00 and 02:15, Aoba, Kinugasa, and Kako joined Chōkai in pounding Astoria, destroying the cruiser's engine room and bringing the flaming ship to a halt.

Quincy had also seen the aircraft flares over the southern ships, received Patterson's warning, had just sounded general quarters and was coming alert when the searchlights from the Japanese column came on.

On questioning him I found out that the Captain, who at that time was laying [sic] near the wheel, had instructed him to beach the ship and he was trying to head for Savo Island, distant some four miles (6 km) on the port quarter.

Mikawa was probably aware that the Japanese Navy had no more heavy cruisers in production and thus would be unable to replace any he might lose to air attack the next day if he remained near Guadalcanal.

Japanese naval commanders took advantage of this by carrying out multiple intense shore bombardments of Allied ground forces at Henderson Field well into late fall 1942.

In hindsight, according to Richard B. Frank, if Mikawa had elected to risk his ships and go after the Allied transports on the morning of 9 August, he could have improved the chances of Japanese victory in the Guadalcanal campaign at its inception, potentially altering the course of the war in the Pacific.

[1]: 122  The report recommended official censure for Captain Howard D. Bode of the Chicago for failing to broadcast a warning to the fleet of encroaching enemy ships.

The report stopped short of recommending formal action against other Allied officers, including Admirals Fletcher, Turner, McCain, and Crutchley, and Captain Riefkohl.

Bode, upon learning that the report was going to be especially critical of his actions, shot himself in his quarters at Balboa, Panama Canal Zone, on 19 April 1943 and died the next day.

[33] Admiral Turner assessed why his forces were so soundly defeated in the battle: "The Navy was still obsessed with a strong feeling of technical and mental superiority over the enemy.

"[1]: 123 Historian Frank adds that "This lethargy of mind would not be completely shaken off without some more hard blows to (U.S.) Navy pride around Guadalcanal, but after Savo, the United States picked itself up off the deck and prepared for the most savage combat in its history.

King, the commander in chief of the United States Fleet, ordered sweeping changes to be made before ships entered surface combat in the future.