On 15 September Hyakutake at Rabaul learned of Kawaguchi's loss and sent the news to Imperial General Headquarters in Japan. In an emergency meeting, the top Japanese IJA and IJN command staffs decided that, Guadalcanal might develop into the most important battle of the war. The loss affected Japanese operations in other areas of the Pacific. Hyakutake realized that to send sufficient troops and supplies to defeat the Allied forces on Guadalcanal he could not support the major ongoing Japanese attacks on the Kokoda Track in New Guinea.
Hyakutake, with the agreement of General Headquarters, ordered his troops on New Guinea who were within of their goal of Port Moresby to pull back until the Guadalcanal battle was finished. Hyakutake sent more troops to Guadalcanal for another attempt to recapture Henderson Field.
As the Japanese troops gathered west of the Matanikau, the U.S. forces strengthened their Lunga defenses. On 14 September Vandegrift moved another battalion, the 3rd Battalion, 2nd Marine Regiment (3/2), from Tulagi to Guadalcanal. On 18 September an Allied naval convoy delivered 4,157 men from the 3rd Provisional Marine Brigade (the 7th Marine Regiment plus a battalion from the 11th Marine Regiment and some additional support units).
The convoy also delivered 137 vehicles, tents, aviation fuel, ammunition, rations and engineering equipment to Guadalcanal. These new soldiers enabled Vandegrift, beginning on 19 September, to establish an unbroken defence around the Lunga perimeter. While protecting this convoy the aircraft carrier was sunk by the Japanese submarine southeast of Guadalcanal. For a while, this left only one Allied aircraft carrier () in the South Pacific area.
Vandegrift also removed several officers who did not meet his standards and promoted junior officers who had done well in the battles. Colonel Merritt Edson who was given command of the 5th Marine Regiment.
The air war over Guadalcanal stopped for a while. There were no Japanese air raids between 14 and 27 September due to bad weather. Both sides reinforced their air units during this time. The Japanese delivered 85 fighters and bombers to their air units at Rabaul while the U.S. brought 23 fighters and attack aircraft to Henderson Field. On 20 September the Japanese had 117 aircraft at Rabaul while the Allies had 71 aircraft at Henderson Field.
The air war got started again with a Japanese air raid on Guadalcanal on 27 September. U.S. Navy and Marine fighters from Henderson Field flew up to try to stop the air raid.
The Japanese began to prepare for their next attempt to recapture Henderson Field. The 3rd Battalion, 4th (Aoba) Infantry Regiment had landed at Kamimbo Bay on the western end of Guadalcanal on 11 September. The battalion had joined Oka's forces near the Matanikau. Deliveries by destroyers on 14, 20, 21 and 24 September brought food and ammunition as well as 280 men from the 1st Battalion, Aoba Regiment, to Kamimbo on Guadalcanal.
The Japanese 2nd and 38th Infantry Divisions were transported from the Dutch East Indies to Rabaul beginning on 13 September. The Japanese planned to transport 17,500 troops from these two divisions to Guadalcanal for the next major attack on the Lunga Perimeter set for 20 October 1942.
Vandegrift was aware that Kawaguchi's troops had retreated to the area west of the Matanikau and that numerous groups of Japanese troops were in the area between the Lunga Perimeter and the Matanikau River. Vandegrift decided to attack the scattered groups of Japanese troops east of the Matanikau.
He also wanted to prevent the main group of Japanese soldiers from strengthening their positions so close to the main Marine defenses at Lunga Point.
The first U.S. Marine attack between 23 and 27 September used soldiers from three U.S. Marine battalions. The attack on Japanese forces west of the Matanikau, was defeated by Kawaguchi's troops under Akinosuke Oka's command. During the fight, three Marine companies were surrounded by Japanese forces and they had many dead and wounded. They escaped with help from the destroyer and landing craft piloted by U.S. Coast Guard personnel.
In the second attack between 6 and 9 October a larger force of Marines crossed the Matanikau River, attacked newly landed Japanese forces from the 2nd Infantry Division under the command of generals Masao Maruyama and Yumio Nasu. The Marines inflicted caused a lot of deaths and wounding for the Japanese 4th Infantry Regiment.
The second attack forced the Japanese to retreat from their positions east of the Matanikau. This caused problems with Japanese plans to do a major attack on the U.S. Lunga defenses.
Between 9 and 11 October the U.S. 1st Battalion 2nd Marines attacked two small Japanese outposts about east of the Lunga perimeter at Gurabusu and Koilotumaria near Aola Bay. The attacks killed 35 Japanese at a cost of 17 Marines and three U.S. Navy personnel.
Throughout the last week of September and the first week of October, Japanese destroyers delivered troops from the Japanese 2nd Infantry Division to Guadalcanal. The Japanese Navy promised to support the Army's attack by delivering troops, equipment, and supplies to the island and doing more air attacks on Henderson Field and sending warships to bomb the airfield.
Millard F. Harmon, commander of United States Army forces in the South Pacific, thought that U.S. Marine forces on Guadalcanal needed new soldiers if the Allies were to defend the island from the next Japanese attack. On 8 October, the 2,837 men of the 164th Infantry Regiment from the U.S. Army's Americal Division boarded ships to Guadalcanal. To protect the transports carrying the 164th to Guadalcanal, Task Force 64 was told to go with the transports. This task force consisted of four cruisers and five destroyers under U.S. Rear Admiral Norman Scott.
They were told to attack any Japanese ships that approached Guadalcanal.
Mikawa's 8th Fleet staff scheduled a large and important destroyer delivery for the night of 11 October. Two seaplane tenders and six destroyers were to deliver 728 soldiers plus artillery and ammunition to Guadalcanal. At the same time, three heavy cruisers and two destroyers under the command of Rear Admiral Aritomo Gotō were to bomb Henderson Field to destroy the CAF and the airfield.
Because U.S. Navy warships had never tried to stop any Tokyo Express missions to Guadalcanal, the Japanese were not expecting any opposition from Allied naval ships that night.
Just before midnight, Scott's warships detected Gotō's force on radar near Guadalcanal. Scott's force was in a position to fire on Gotō's ships. Opening fire, Scott's warships sank one of Gotō's cruisers and one of his destroyers, heavily damaged another cruiser, seriously wounded Gotō, and forced the rest of Gotō's warships to abandon the bombing mission and retreat.
One of Scott's destroyers was sunk and one cruiser and another destroyer were heavily damaged. The Japanese supply convoy unloaded at Guadalcanal and began its return journey without being discovered by Scott's force. Later on the morning of 12 October, four Japanese destroyers from the supply convoy turned back to help Gotō's damaged warships.
Air attacks by CAF aircraft from Henderson Field sank two of these destroyers later that day. The convoy of U.S. Army troops reached Guadalcanal as scheduled the next day and delivered its cargo and passengers to the island.
Even after the U.S. victory off Cape Esperance, the Japanese continued with plans for a large attack later in October. The Japanese decided to risk not using fast warships to deliver their men and supplies to the island.
On 13 October, a convoy of six cargo ships with eight destroyers left the Shortland Islands for Guadalcanal. The convoy carried 4,500 troops from the 16th and 230th Infantry Regiments, some naval marines, two batteries of heavy artillery, and one company of tanks.