Operation Battle of Edson's Ridge

The 'Battle of Edson’s Ridge., sometimes known as the 'Battle of the Bloody Ridge', 'Battle of Raiders Ridge' and 'Battle of the Ridge', was a battle fought between Japanese and US forces as the second of three major Japanese ground offensives on Guadalcanal during the US 'Watchtower' campaign to land on, take and hold that island of the Solomon islands group (12/14 September 1942).

In this battle, men of the US Marine Corps, under the overall command of Major General Alexander A. Vandegrift, repulsed an attack by the Japanese 35th Brigade under the command of Major General Kiyotake Kawaguchi. The marines were defending the Lunga sector of the defensive perimeter which shielded Henderson Field, the airfield which had been captured from the Japanese in the initial 'Watchtower' landings on 7 August 1942. Kawaguchi’s unit had been despatched Guadalcanal in response to the Allied landings with the specific mission of recapturing the airfield and driving the Allied forces from the island.

Underestimating the strength of the Allied forces on Guadalcanal, which was about 12,000 men, Kawaguchi’s 6,000 troops conducted several nocturnal frontal assaults on the US defences. The main Japanese assault occurred around Lunga ridge to the south of Henderson Field, an area held be men of several marine units, primarily troops of the 1st Raider Battalion and 1st Parachute Battalion under the command of Lieutenant Colonel Merritt A. Edson. Although the marine defences were almost overrun, Kawaguchi’s attack was ultimately defeated, with heavy losses for the Japanese.

Because of the key part played by Edson’s unit in defending it, the ridge has become known as 'Edson’s Ridge' in historical accounts of the battle. After the 'Battle of Edson’s Ridge', the Japanese continued to send troops to Guadalcanal for further attempts to retake Henderson Field, affecting Japanese offensive operations in other areas of the South Pacific.

On 7 August 1942, Allied (primarily US) forces had landed on Guadalcanal, Tulagi and Florida islands in the Solomon islands group. The landings were meant to deny their use by the Japanese as bases from which to threaten the maritime supply routes between the USA and Australia. The landings were also intended to secure the islands as starting points for an Allied campaign to neutralize the major Japanese base at Rabaul on New Britain island and to support the Allied campaign on New Guinea.

The landings took the Japanese by total operational and tactical surprise, and by the fall of night on 8 August the Allied landing forces had secured Tulagi and nearby small islands, as well as an airfield under construction at Lunga Point on the northern coast of Guadalcanal. By 9 August, 10,900 men of Vandegrift’s 1st Marine Division were ashore on Guadalcanal, occupying a loose perimeter around the Lunga Point area. On 12 August, the airfield was named Henderson Field after Major Lofton Henderson, a marine pilot who had been killed in the 'Battle of Midway'. The Allied aircraft and pilots who then operated out of Henderson Field were called the Cactus Air Force after the Allied codename for Guadalcanal island.

In response to the Allied landings on Guadalcanal, the Japanese Imperial General Headquarters assigned the the corps-sized 17th Army, based at Rabaul and commanded by Lieutenant General Harukichi Hyakutake, the task of retaking Guadalcanal. Already heavily involved with the Japanese campaign in New Guinea, the 17th Army had available only a few units to send to the southern part of the Solomon islands group. Of these units, Kawaguchi’s 35th Brigade was currently in the Palau islands group, the 4th Regiment was in the Philippine islands group and Lieutenant Colonel Kiyonao Ichikis 28th Regiment was embarked on transport vessels near Guam in the Mariana islands group. These different units immediately began to move toward Guadalcanal. Ichiki’s regiment, the closest of the three units, arrived first, and the initial element of the regiment, comprising about 917 men, landed from destroyers at Taivu Point, about 18 miles (29 km) to the east of the Lunga perimeter, on 19 August.

Wholly underestimating the strength of the Allied forces on Guadalcanal, Ichiki’s first element conducted a nocturnal assault on marine positions at Alligator Creek on the eastern side of the Lunga perimeter in the early morning hours of 21 August. The Japanese assault was repulsed with devastating losses for the attackers in what became known as the 'Battle of the Tenaru River': all but 128 of the 917 men (including Ichiki) were killed in the battle. The survivors returned to Taivu Point, notified 17th Army's headquarters of their defeat and awaited further reinforcements and orders from Rabaul.

By 23 August, Kawaguchi’s unit had reached Truk in the Caroline islands group and was loaded onto slow transport ships for the rest of the trip to Guadalcanal. Because of the damage caused by Allied air attack to a separate troop convoy during the 'Battle of the Eastern Solomons', the Japanese decided to deliver Kawaguchi’s troops not to Guadalcanal by slow transport ship but rather to Rabaul. The Japanese planned to deliver Kawaguchi’s men thence to Guadalcanal by high-speed destroyers, staging through a Japanese naval base in the Shortland islands group. The destroyers were usually able to make the round trip down 'The Slot' to Guadalcanal and back in a single night, thereby minimising their exposure to Allied air attack. However, most of the soldiers' heavy equipment and supplies, such as heavy artillery, vehicles and much of their food and ammunition, could not be taken to Guadalcanal with them. These high-speed destroyer runs to Guadalcanal, which occurred throughout the campaign, were later called the 'Tokyo Express' by the Allied forces and 'Rat Transportation' by the Japanese, who controlled the seas around the Solomon islands group during by night and were not challenged by the Allies. However, any Japanese ship remaining within the 200-mile (320-km) range of the aircraft operating from Henderson Field in daylight was in great danger from air attacks. This 'curious tactical situation' continued for several months.

On 28 August, 600 of Kawaguchi’s men were loaded onto the destroyers Asagiri, Amagiri, Yugiri and Shirakumo of Destroyer Division 20. Because of a shortage of fuel, these destroyers could not make the entire round trip to and from Guadalcanal at high speed in one night, and had therefore to start the trip earlier in the day so that they could complete the trip by the next morning at a slower and therefore more fuel-economical speed. At 18.05 that day, 11 US dive-bombers from the marines' VMSB-232 squadron, under the command of Lieutenant Colonel Richard Mangrum, flew from Henderson Field and located and attacked the Japanese destroyers about 70 miles (110 km) tp the north of Guadalcanal, sinking Asagiri and heavily damaging Yugiri and Shirakumo. Amagiri took Shirakumo in tow and the three destroyers returned to the Shortland islands group without completing their mission. The attack on the destroyers killed 62 of Kawaguchi’s men and 94 members of the ships' crews.

Subsequent 'Tokyo Express' undertakings were more successful. Between 29 August and 4 September, various Japanese light cruisers, destroyers and patrol boats were able to land almost 5,000 men at Taivu Point, this total including the whole of the 35th Brigade, one battalion of the 44th Regiment and the rest of Ichiki’s regiment. Kawaguchi landed at Taivu Point on 31 August, and commanded all the Japanese troops on Guadalcanal. During the night of 4/5 September, as the 'Tokyo Express' destroyers Yudachi, Hatsuyuki and Murakumo prepared to shell Henderson Field after landing their troops, they detected and sank two US ships, the small and elderly destroyer transports Little and Gregory, which were being used to shuttle Allied troops around the area of Guadalcanal and Tulagi islands.

Despite the successes of the destroyer runs, Kawaguchi insisted that as many of his brigade’s men as possible be delivered to Guadalcanal by slow barges. Therefore, a convoy of 61 barges carrying 1,100 troops and heavy equipment, mainly of the 2nd Battalion of Colonel Akinosuka Oka’s 124th Regiment, departed the northern coast of Santa Isabel island on 2 September. On 4/5 September, aircraft from Henderson Field attacked the barge convoy, killing about 90 of the soldiers and destroying much of the unit’s heavy equipment. Most of the remaining 1,000 troops were able to land near Kamimbo, to the west of the Lunga perimeter over the next few days. By 7 September, Kawaguchi had 5,200 troops at Taivu Point and 1,000 to the west of the Lunga perimeter, and was confident enough that he could defeat the Allied forces facing him that he declined a 17th Army offer for delivery of one more infantry battalion to augment his forces. Kawaguchi believed that there were only about 2,000 US Marines on Guadalcanal.

During this time, Vandegrift continued to direct efforts to boost the defenses of the Lunga perimeter. Between 21 August and 3 September, he relocated three marine battalions, including Edson’s 1st Raider Battalion and the 1st Parachute Battalion, from Tulagi and Gavutu to Guadalcanal. These units added about 1,500 men to Vandegrift’s original 11,000 men defending Henderson Field. The 1st Parachute Battalion, which had suffered heavy casualties in the 'Battle of Tulagi and Gavutu-Tanambogo' in August, was placed under Edson’s command.

Kawaguchi set 12 September as the date for his attack on the Lunga perimeter and began marching his force to the west from Taivu Point toward Lunga Point on 5 September. He sent a radio message to the 17th Army requesting that it make air attacks on Henderson Field from 9 September, and that warships be stationed off Lunga Point on 12 September to 'destroy any Americans who attempted to flee from the island'. On 7 September, Kawaguchi issued his attack plan to 'rout and annihilate the enemy in the vicinity of the Guadalcanal Island airfield'. Kawaguchi’s plan called for his force to divide into three, approach the Lunga perimeter inland, and launch a surprise night attack. Oka’s force was to attack the perimeter from the west while Ichiki’s second echelon, now renamed ther 'Kuma' Battalion attacked attack from the east. The main attack would be made by Kawaguchi’s Centre Body of 3,000 men in three battalions, from the south of the Lunga perimeter. By 7 September, most of Kawaguchi’s troops had started their approach march from Taivu Point toward Lunga Point along the coast, leaving behind about 250 men to guard the brigade’s supply base at Taivu Point.

Meanwhile, native island scouts, directed by Martin Clemens, a British colonial official and officer in the British Solomon Islands Protectorate Defence Force, had informed the marines of the presence of Japanese troops just to the west of Taivu Point, near the village of Tasimboko, about 17 miles (27 km) to the east of Lunga Point. Edson launched a raid against these Japanese troops. The destroyer transports McKean and Manley and two patrol boats ferried 813 of Edson’s men to Taivu in two trips. Edson and his first wave of 501 men landed at Taivu at 05.20 on 8 September. Supported by aircraft from Henderson Field and gunfire from the destroyer transports, Edson’s men advanced towards Tasimboko village but were slowed by Japanese resistance. At 11.00, the rest of Edson’s men landed. With this reinforcement and more support from the Henderson Field aircraft, Edson’s force pushed into the village. The Japanese defenders, believing a major landing was under way after seeing the concurrent approach of an Allied supply ship convoy heading towards Lunga Point, retreated into the jungle, leaving behind 27 dead. Two marines were killed.

In Tasimboko, Edson’s troops discovered the supply base for Kawaguchi’s forces, including large stockpiles of food, ammunition, medical supplies and a short-wave radio. The marines seized documents, equipment and food, destroyed the rest, and returned to the Lunga perimeter at 17.30. The quantities of supplies and intelligence from the captured documents revealed that at least 3,000 Japanese troops were on the island and apparently planning an attack.

Edson and Colonel Gerald C. Thomas, Vandegrift’s operations officer, believed that the Japanese attack would come at the Lunga Ridge, a narrow, grassy coral ridem, some 1,095 yards (1000 m) long, parallel to the Lunga river just to the south of Henderson Field. The ridge offered a natural avenue of approach to the airfield, commanded the area round it and was almost undefended. Edson and Thomas tried to persuade Vandegrift to move forces to defend the ridge, but Vandegrift refused, believing that the Japanese were more likely to attack along the coast. Finally, Thomas convinced Vandegrift that the ridge was a good location for Edson’s Raiders to 'rest' from their actions of the preceding month, and on 11 September, the 840 men of Edson’s force, including the 1st Raiders and the 'paramarines', deployed onto and round the ridge and prepared to defend it.

Kawaguchi’s Centre Body was planning to attack the Lunga perimeter at the ridge, which they called the 'centipede' for its shape. On 9 September, Kawaguchi’s troops left the coast at Koli Point and, divided into four columns, marched into the jungle toward their predesignated attack points to the south and south-east of the airfield. Lack of good maps, at least one faulty compass and almost impenetrable jungle caused the Japanese columns to move slowly and zigzag, costing them considerable time. Over the same period, Oka’s troops approached the Lunga perimeter from the west. Oka had some intelligence on the marine defences, extracted from a US Army pilot captured on 30 August.

During 12 September, Kawaguchi’s troops struggled through the jungle toward their assembly points for that night’s attacks. Kawaguchi wanted his three Centre Body battalions in place by 14.00, but they did not reach their assembly areas until after 22.00. Oka was also delayed in his advance toward the marine lines in the west. Only the 'Kuma' Battalion reported that it was in place on time. Despite the problems in reaching the planned attack positions, Kawaguchi still had confidence in his attack plan because a captured US pilot disclosed the fact that the ridge was the weakest part of the marine defences. Japanese bombers made a daylight attack on the ridge on 11/12 September, causing a few casualties including two men killed.

From the reports by scouts of Solomon islanders and their own patrols, the US forces knew of the approach of the Japanese forces, but did not know exactly where or when they would attack. The ridge around which Edson deployed his men comprises three distinct hillocks: at the southern tip and surrounded on three sides by thick jungle is Hill 80, so named because it rose 80 ft (24 m) above sea level; 600 yards (550 m) to the north is Hill 123, the dominant feature on the ridge' and the northernmost hillock is unnamed and about 60 ft (18 m) high. Edson placed the five companies of his raider battalion on the western side of the ridge and the three parachute battalion companies on the eastern side, holding positions in depth from Hill 80 to Hill 123. Two of the five raider companies, Companies B and C, held a line between the ridge, a small and swampy lagoon, and the Lunga river. Machine gun teams from Company E, which was the heavy weapons company, were scattered throughout the defences. Edson placed his command post on Hill 123.

At 21.30 on 12 September, the Japanese light cruiser Sendai and three destroyers shelled the Lunga perimeter for 20 minutes and illuminated the ridge with a searchlight. Japanese artillery began shelling the marine lines, but did little damage. At the same time, scattered groups of Kawaguchi’s troops began skirmishing with marines around the ridge. Kawaguchi’s 1st Battalion. commanded by Major Yukichi Kokusho, attacked the raider’s Company C between the lagoon and the Lunga river, overrunning at least one platoon and forcing the company to fall back to the ridge. Kokusho’s battalion became entangled with those of Kawaguchi’s 3rd Battalion under Lieutenant Colonel Kusukichi Watanabe, who were still struggling to reach their attack positions, and the resulting confusion effectively stopped that night’s Japanese attack on the ridge. Kawaguchi, who was having trouble locating where he was in relation to the marine lines as well as in the co-ordination of his troops' attacks, later complained that 'Due to the devilish jungle, the brigade was scattered all over and was completely beyond my control. In my whole life I have never felt so disappointed and helpless.' Twelve marines were killed, while the Japanese casualties are unknown but perhaps somewhat greater. Although both Oka in the west and the 'Kuma' Battalion in the east tried to attack the marine lines that night, they failed to make contact and halted near the marine lines at dawn.

At first light on 13 September, Cactus Air Force aircraft and marine artillery fired into the area just to the south of the ridge, forcing any Japanese out in the open to seek cover in the nearby jungle. The Japanese suffered several casualties, including two officers of Watanabe’s battalion. At 05.50, Kawaguchi decided to regroup his forces for another attack that night.

Expecting the Japanese to attack again that night, Edson ordered his men to improve their defences on and around the ridge. After a failed attempt by two companies to retake the ground on the marines' right flank lost to Kokusho’s battalion during the previous night, Edson repositioned his forces. He pulled his front back about 400 yards (365 m) to a line that stretched 1,800 yards (1645 m), starting at the Lunga river and crossing the ridge about 150 yards (135 m) to the south of Hill 123. Around and behind Hill 123 he placed five companies. Any Japanese attackers attempting to reach the top of Hill 80 would have to advance more than 400 yards (365 m) of open terrain to close with the marine positions at Hill 123. With just a few hours to prepare, the marines were able to construct only rudimentary and shallow field fortifications. They were low on ammunition, with one or two grenades for each marine. Vandegrift ordered a reserve force, comprising the 2/5th Marines to move into a position just to the rear of Edson’s troops. In addition, a battery of four 105-mm (4.13-in) howitzers from the 3/11th Marines, under the command of Lieutenant Colonel James J. Keating, moved to a location from which it could provide direct fire onto the ridge, and a forward artillery observer was placed with Edson’s front-line units.

Late in the afternoon, Edson mounted a grenade box and addressed his exhausted troops with the words 'You men have done a great job, and I have just one more thing to ask of you. Hold out just one more night. I know we’ve been without sleep a long time. But we expect another attack from them tonight and they may come through here. I have every reason to believe that we will have reliefs here for all of us in the morning.'

As night fell on 13 September, Kawaguchi faced Edson’s 830 marines with his brigade’s 3,000 men and an assortment of light artillery. The night was very dark, with no moon. At 21.00, seven Japanese destroyers briefly bombarded the ridge. Kawaguchi’s attack began just after the sun had set, with Kokusho’s battalion assaulting the raiders' Company B on the marines' right flank, just to the west of the ridge. The force of the assault caused Company B to fall back to Hill 123. Under marine artillery fire, Kokusho reassembled his men and continued his attack. Without pausing to try to roll up the other nearby marine units, whose flanks were now unprotected, Kokusho’s unit moved forward through the low swampy land between the ridge and the Lunga river, heading for the airfield. Kokusho’s men came upon a pile of marine supplies and rations and, not having eaten adequately for two days, paused to gorge themselves on the C and K rations. Kokusho ordered his men to continue the attack, and at about 03.00 led them against the marine units round the northern portion of the ridge, just short of the airfield, as well as Hill 123. In the heavy fighting that followed, Kokusho and around 100 of his men were killed, ending that attack.

Meanwhile, Kawaguchi’s 2nd Battalion, under the command of Major Masao Tamura, assembled for its assault on Hill 80 from the jungle to the south of the ridge. Marine observers spotted Tamura’s preparations and called in artillery fire, and at about 22.00 a barrage from 12 105-mm (4.13-in) howitzers hit Tamura’s position. In response, two of Tamura’s companies, totalling about 320 men, charged up Hill 80 with fixed bayonets behind their own barrage of mortar fire and grenades. Tamura’s attack hit Company B of the parachute battalion and also the raiders Company B, pushing the former off the eastern side of the ridge into a draw below the ridgeline. To protect the exposed Company B, Edson immediately ordered it to pull back onto Hill 123.

At the same time, a company of Watanabe’s battalion infiltrated through a gap between the eastern side of the ridge and parachute battalion’s Company C. Deciding that their positions were now untenable, the parachute battalion’s Companies B and C climbed onto the ridge and retreated to a position behind Hill 123. In the darkness and confusion of the battle, the retreat quickly became confused and disorganised. A few marines began shouting that the Japanese were attacking with poison gas, scaring other marines who no longer possessed their gas masks. After arriving behind Hill 123, some of the marines continued on toward the airfield, repeating the word 'withdraw' to anyone within earshot, and other marines began to follow them. Just at the moment that it appeared that the marines on the hill were about to break and head for the rear, Edson, Major Kenneth D. Bailey from Edson’s staff, and other marine officers appeared and, with 'vivid' language, herded the marines back into defensive positions around Hill 123.

As the marines formed into a horseshoe-shaped line around Hill 123, Tamura’s battalion began a series of frontal assaults, charging up the saddle from Hill 80 and up from below the eastern side of the ridge. Under the light of flares dropped by at least one Japanese floatplane, the marines repulsed the first two attacks by Tamura’s men. Tamura’s troops hoisted a 75-mm (2.95-in) gun to the top of Hill 80 in an effort to fire directly at the marines, but the gun had a faulty firing pin. At 00.00, during a short lull in the fighting, Edson ordered parachute Companies B and C to advance from behind Hill 123 to strengthen his left flank. With fixed bayonets, the paramarines swept forward, killing Japanese soldiers who had overrun the marine lines and were apparently preparing to roll up the marines from the flank, and took position on the eastern side of the hill. Marines from other units, as well as members of Edson’s command staff carried ammunition and grenades under fire to Hill 123, where the marines were running critically low.

The Japanese fell on Edson’s left flank just after the paramarines had taken position, but were again stopped by marine rifle, machine gun, mortar and grenade fire. Marine 105-mm (4.13-in) and 75-mm (2.95-in) artillery was also taking a heavy toll on the attackers. A captured Japanese soldier later said that his unit was wholly destroyed by the marines' artillery fire, which only one man in ten of his company survived.

By 04.00, after withstanding several more assaults, of which some involved hand-to-hand combat, and severe sniper fire from all sides, Edson’s men were joined by men of the 2/5h Marines, who helped repulse two more Japanese attacks before dawn. Throughout the night, as Kawaguchi’s men came close to overrunning the marine defences, Edson remained standing about 20 yards (18 m) behind the marine firing line on Hill 123, exhorting his troops and directing their defensive efforts. In the course of the heavy fighting, portions of three Japanese companies, including two from Tamura’s and one from Watanabe’s battalions, bypassed the marine defences on the ridge, while suffering heavy losses from marine fire, and reached the edge of 'Fighter One', a secondary runway of Henderson Field. A counterattack by the marine engineers stopped one Japanese company’s advances and forced it to retreat. The other two companies waited at the edge of the jungle for reinforcements to arrive before attacking into the open area around the airfield. When no reinforcements joined them, both companies fell back after the break of day to their original positions to the south of the ridge. Most of the rest of Watanabe’s battalion did not participate in the battle because they had lost contact with their commander during the night.

At the break of day on 14 September, pockets of Japanese soldiers remained scattered along both sides of the ridge. But with Tamura’s battalion shattered after losing three-quarters of its officers and men, and with heavy casualties to his other attacking units, Kawaguchi’s assault on the ridge had effectively ended. About 100 Japanese soldiers still remained in the open on the southern slope of Hill 80, perhaps preparing for one more charge on Hill 123. At first light, three Bell P-400 Airacobra single-engined fighters of the USAAF’s 67th Fighter Squadron, acting on a request personally delivered by Bailey of Edson’s staff, strafed the Japanese near Hill 80 and killed most of them, the few survivors retreating back into the jungle.

As the battle on the ridge took place, the units led by Kuma and Oka also attacked the marine defences on the eastern and western sides of the Lunga perimeter. The 'Kuma' Battalion, under the command of Major Takeshi Mizuno, attacked the south-eastern sector of the Lunga perimeter, defended by men of the 3/1st Marines. Mizuno’s attack started at about 00.00, with one company attacking through marine artillery fire and getting to the stage of hand-to-hand combat with the marine defenders before being thrown back. Mizuno was killed in this attack. After daybreak, believing that the rest of Mizuno’s battalion was still in the area, the marines sent forward six light tanks without infantry support to sweep the area in front of the marine lines: four Japanese 37-mm (1.46-in) anti-tank guns destroyed or disabled three of the tanks, and while some of these vehicles' crewmen were able to escape the flames, several of them were bayoneted and killed by the Japanese. One tank tumbled down an embankment into the Tenaru river, drowning its crew. At 23.00 on 14 September, the remnants of the 'Kuma' Battalion made another attack on the same portion of the marine lines, but were repulsed. A final attack by the 'Kuma' Battalion during the evening of 15 September was also driven back.

Oka’s unit of about 650 men attacked the marines at several locations on the western side of the Lunga perimeter. At about 04.00 on 14 September, two Japanese companies attacked positions held by the 3/5th Marines near the coast and were thrown back with heavy losses. Another Japanese company captured a small ridge slightly farther inland but was then pinned down by marine artillery fire throughout the day and took heavy losses before withdrawing during the evening. The rest of Oka’s unit failed to find the marine lines and did not participate in the attack.

At 13.05 on 14 September, Kawaguchi led the survivors of his shattered brigade away from the ridge and deeper into the jungle to rest and tend their wounded throughout the following day. Kawaguchi’s units were then ordered to withdraw west to the Matanikau river valley to link with Oka’s unit, a 6-mi (9.7-km) march over difficult terrain. Kawaguchi’s troops began the march on the morning of 16 September, and almost every soldier able to walk had to help carry the wounded. As they marched, the exhausted and hungry soldiers, who had eaten their last rations on the morning before their withdrawal, began to discard their heavy equipment and then their rifles. By the time most of them reached Oka’s positions at Kokumbona five days later, only half still carried their weapons. The 'Kuma' Battalion's survivors, attempting to follow Kawaguchi’s Centre Body, became lost, wandered for three weeks in the jungle, and almost starved to death before finally reaching Kawaguchi’s camp.

In total, Kawaguchi’s force lost about 830 killed in the attack, including 350 in the 'Tamura' Battalion, 200 in the 'Kokusho' Battalion, 120 in Oka’s force, 100 in the 'Kuma' Battalion and 60 in the 'Watanabe' Battalion. An unknown number of wounded also died during the withdrawal to the Matanikau river. On and around the ridge, the marines counted 500 Japanese bodies, including 200 on the slopes of Hill 123. The marines themselves suffered 80 men killed between 12 and 14 September.

On 17 September, Vandegrift sent two companies of the 1/1st Marines to pursue the retreating Japanese. The marines were ambushed by two Japanese companies serving as the withdrawal’s rearguard, and one marine platoon was pinned down as the rest of the marines retreated. The marine company commander requested permission to attempt to rescue his platoon but was denied by Vandegrift, and by the fall of night the Japanese had overran and nearly annihilated the platoon, killing 24 marines with only a few of the platoon’s wounded members surviving. On 20 September, a patrol from Edson’s Raiders encountered stragglers from Kawaguchi’s retreating column and called in artillery fire that killed 19 of them.

As the Japanese regrouped in the area to the west of the Matanikau river, the US forces concentrated on shoring up and strengthening their Lunga defences. On 14 September, Vandegrift moved another battalion, the 3/2nd Marines, from Tulagi to Guadalcanal. On 18 September, an Allied naval convoy delivered 4,157 men of the 3rd Provisional Marine Brigade, comprising the 7th Marines augmented by additional support units, to Guadalcanal. These reinforcements allowed Vandegrift, from 19 September, to establish an unbroken Defence line round the Lunga perimeter. Vandegrift’s forces' next significant clashes with the Japanese occurred along the Matanikau river on 23/27 September and 6/9 October.

It was on 15 September in Rabaul that Hyakutake learned of Kawaguchi’s defeat, which was the Imperial Japanese army’s first defeat involving a unit of this size in the Pacific War. Hyakutake forwarded the news to the Imperial General Headquarters. In an emergency session, the top Japanese army and navy command staffs concluded that 'Guadalcanal might develop into the decisive battle of the war'. The results of the battle began to have a telling strategic impact on Japanese operations in other areas of the Pacific. Hyakutake realised that, in order to send sufficient troops and matériel to defeat the Allied forces on Guadalcanal, he could no longer support the major Japanese offensive on the Kokoda Track in New Guinea. With the agreement of the Imperial General Headquarters, Hyakutake ordered his troops in New Guinea, who were within 30 miles (48 km) of their objective of Port Moresby, to withdraw until the situation on Guadalcanal had been resolved. The Japanese were not able to resume their drive toward Port Moresby, so their defeat at Edson’s Ridge contributed not only to Japan’s defeat in the Guadalcanal campaign, but also to Japan’s ultimate defeat throughout the South Pacific.

After delivering more forces during the next month, the Japanese launched a major ground offensive on Guadalcanal, led by Hyakutake, late in October 1942 at the 'Battle for Henderson Field', but this resulted in an even more decisive Japanese defeat.