Operation Battle of Mt Austen, the Galloping Horse and the Sea Horse

The 'Battle of Mt Austen, the Galloping Horse and the Sea Horse', of which a part is sometimes known as the 'Battle of the Gifu', was fought by primarily US forces and the Japanese in the hills near the Matanikau river area on Guadalcanal during the Solomon islands campaign (15 December 1942/23 January 1943).

The forces of the US XIV Corps were under the overall command of Major General Alexander McC. Patch and the Japanese forces were elements of the 17th Army under the command of Lieutenant General Harukichi Hyakutake.

In the battle, men of the US Army and US Marine Corps, assisted by small but highly effective numbers of native Solomon islanders, attacked the Japanese forces defending well-fortified and entrenched positions on several hills and ridges. The most prominent hills were called Mt Austen, the Galloping Horse and the Sea Horse by the Americans. At this time in the later stages if the Guadalcanal campaign, the US forces were seeking to destroy the Japanese forces on the island and the Japanese were attempting to hold their defensive positions until they could be reinforced.

Both sides experienced extreme difficulties in living and fighting in the thick jungles and tropical environment of the battle area. Many of the US troops were also involved in their first combat operations. The Japanese were mostly cut off from resupply and suffered greatly from malnourishment and lack of medical care. After some difficulty, the US forces succeeded in taking Mt Austen, in the process reducing a strongly defended position called the Gifu, as well as the Galloping Horse and the Sea Horse. In the meantime, the Japanese decided to abandon Guadalcanal and withdrew to the island’s west coast, from which most of the surviving Japanese troops were successfully evacuated in 'Ke' (i) during the first week of February 1943.

On 7 August 1942, eight months after the beginning of the Pacific War, Allied (primarily US) forces mde their 'Watchtower' and 'Ringbolt' landings on Guadalcanal, Tulagi and Florida islands in the Solomon islands group. These landings were designed to deny their use by the Japanese as bases from which to threaten the Allied maritime supply routes between the USA and Australia, and to secure the islands as starting points for a campaign with the eventual goal of isolating the major Japanese base at Rabaul on New Britain island while at the same time also supporting the Allied campaign in New Guinea. The landings began the six-month Guadalcanal campaign.

Having already made their initial landings on the islands, the Japanese were taken by surprise by 'Watchtower' and 'Ringbolt'. By the fall of nightl on 8 August, the 11,000 Allied troops, mainly of Major General Alexander A. Vandegrift’s US 1st Marine Division, had secured Tulagi and nearby small islands as well as the Japanese airfield (later named Henderson Field) under construction at Lunga Point on Guadalcanal. Allied aircraft operating from Henderson Field were called the 'Cactus Air Force' after the Allied codename for Guadalcanal. To protect the airfield, the US Marines established a perimeter defence around Lunga Point. Additional reinforcements over the next two months later increased the number of US troops at Lunga Point to more than 20,000 men.

In response to the Allied landing on Guadalcanal, the Japanese Imperial General Headquarters assigned to Hyakutake’s 17th Army, which a corps-sized formation based at Rabaul, the task of retaking Guadalcanal. Formations and units of the 17th Army began to reach Guadalcanal on 19 August at the start of the Japanese attempt to drive the Allied forces from the island.

Because of the threat posed by Cactus Air Force warplanes based at Henderson Field, the Japanese were unable to use large, slow transport ships to deliver troops and supplies to the island, and instead used warships based at Rabaul and the Shortland islands group to carry their forces to Guadalcanal. The Japanese warships, which were mainly light cruisers and destroyers of Vice Admiral Gunichi Mikawa’s 8th Fleet, were usually able to make the round trip down 'The Slot' to Guadalcanal and back in a single night, thereby minimizing their exposure to Cactus Air Force attack. Delivering the troops in this manner, however, prevented the carriage of most of the troops' heavier equipment and supplies, such as heavy artillery, vehicles, and much food and ammunition, from being carried to Guadalcanal with them. These high-speed warship runs to Guadalcanal continued throughout the campaign and were later called the 'Tokyo Express' by the Allies and 'Rat Transportation' by the Japanese.

Using forces delivered to Guadalcanal in this manner, the Japanese made three unsuccessful attempts to retake Henderson Field. First, a reinforced battalion of the 28th Regiment was defeated in the 'Battle of the Tenaru' on 21 August; second, Major General Kiyotake Kawaguchi’s augmented 35th Brigade was defeated in the 'Battle of Edson’s Ridge' on 12/14 September; and third, Lieutenant General Masao Maruyama’s 2nd Division, augmented by one regiment of Lieutenant General Tadayoshi Sano’s 38th Division was defeated with heavy losses in the 'Battle for Henderson Field' on 23/26 October.

Throughout the campaign, the Japanese used Mt Austen (called Bear Height by the Japanese and Mt Mambulu by the local Solomon islanders), to the west of the Lunga river and about 6 miles (9.7 km) from Henderson Field, to observe the US defences around Lunga Point. Artillery emplaced on Mt Austen delivered harassing fire on Henderson Field, and the hill was also used as a defensive point for the protection of the Japanese positions around the upper reaches of the Matanikau river valley as well as to protect the 'Maruyama Road', which was a trail used by the Japanese to move men and supplies into the interior of the island. Mt Austen, with its summit at 1,514 ft (461 m), was not a single peak but rather a mixed ridgeline of rocky, exposed and jungle-covered ridges and hilltops. After the defeat in the 'Battle for Henderson Field', the Army Section of the Imperial General Headquarters ordered Hyakutake to increase the numbers of troops and artillery emplaced on the ridgeline to help in preparations for the next planned attack on the Americans. Hyakutake therefore directed some of the units retreating from the Henderson Field battle area to fortify Mt Austen and nearby hilltops. The forces deployed to Mt Austen included Colonel Akinosuka Oka’s 124th Regiment and several artillery units. Later, surviving elements of the 230th Regiment, which had sustained heavy losses during the Koli Point action and subsequent retreat, joined Oka’s forces around Mt Austen.

On 5, 7 and 8 November, 'Tokyo Express' missions landed most of the 38th Division's 228th Regiment and the 1/229th Regiment on Guadalcanal. On 10 November, Japanese destroyers landed Sano, the commander of the 38th Division, plus his staff and 600 more men of Sano’s division. Hyakutake used the newly arrived troops to help stop a US attack to the west of the Matanikau river on 8/11 November, then sent the units of the 228th Regiment and 229th Regiment on 11 November to reinforce Oka’s forces. Major General Takeo Ito, commander of the 38th Division's infantry group, later took command of the defences around Mt Austen.

A Japanese attempt to deliver the rest of the 38th Division and its heavy equipment failed during the naval Battle of Guadalcanal on 12/15 November. Only some 2,000 to 3,000 of the division’s remaining 7,000 men reached the island and most of their supplies, ammunition, and equipment was lost. Because of this failure, the Japanese cancelled their next planned attempt to recapture Henderson Field.

By the beginning of December, the Japanese were facing greater difficulty in keeping their troops on Guadalcanal supplied because of Allied air and naval attacks on the Japanese supply chain of ships and bases. The few supplies delivered to the island were not enough to sustain Japanese troops who, by 7 December, were losing about 50 men each day to the effects of malnutrition, disease and the combination of Allied ground and air attacks. The Japanese had delivered almost 30,000 troops to Guadalcanal since the campaign began, but by December only some 20,000 of that number were still alive. Of those 20,000, only about 12,000 remained at all capable of combat duty. On 12 December, the Japanese navy proposed that Guadalcanal be abandoned. Despite opposition from the Japanese army leadership, which still hoped that Guadalcanal could eventually be retaken from the Allies, Imperial General Headquarters, with approval from the Emperor Hirohito, on 31 December agreed to the evacuation of all Japanese forces from the island and the establishment of a new line of defence for the Solomon islands on New Georgia. The Japanese allocated the designation 'Ke' (i) to the evacuation effort and planned to execute the operation beginning on 14 January 1943.

Meanwhile, the USA continued to deliver additional troops to Guadalcanal. The three regiments of Patch’s Americal Division (the 164th, 182nd and 132nd Infantry) were delivered to Guadalcanal on 13 October, 12 November and 8 December respectively. In addition, the independent 147th Infantry and the 8th Marines, the latter of Major General C. F. B. Price’s 2nd Marine Division landed on 4 November. The reinforcements also included additional artillery, air, support and construction units.

On 9 December, Patch succeeded Vandegrift as commander of Allied forces on Guadalcanal and Tulagi. Onthat same day, the 5th Marines left the island, followed by the rest of the 1st Marine Division by the end of the month. Patch was ordered to eliminate all Japanese forces remaining on Guadalcanal. Patch told his superior, Lieutenant General Millard F. Harmon, commander of all US Army forces in the South Pacific Area, that he needed more troops to accomplish the task. In response, Harmon ordered Major General J. Lawton Collins’s 25th Division, currently in the process of redeploying from Hawaii to the South Pacific Area, to be shipped directly to Guadalcanal, the division’s units arriving on Guadalcanal in stages during the last two weeks of December and the first week of January 1943. In addition, the rest of the 2nd Marine Division’s units, including the 6th Marines, were ordered to Guadalcanal during the same period. By 7 January, the US forces on Guadalcanal totalled slightly more than 50,000 men.

On 12 December, a small force of the 38th Field Engineer Regiment infiltrated the US lines from the south, destroying one fighter and a fuel truck on Henderson Field before escaping. Two days later, a US Army patrol of the 132nd Infantry skirmished with a group of Japanese on the eastern slopes of Mt Austen. On 15 December, in yet another night infiltration raid onto Henderson Field, a Lieutenant Ono led four men equipped with picric acid blocks past US sentry positions and destroyed several Bell P-39 Airacobra fighters. Throughout the Guadalcanal campaign, Japanese forces continued night infiltration tactics against US forces, but these led to few US casualties.

Patch was sure that these events illustrated an unacceptable level of risk to Henderson Field by Japanese troops on and around nearby Mt Austen, however, and on 16 December, in preparation for a planned general offensive to destroy all Japanese forces remaining on Guadalcanal, Patch elected to secure the Mt Austen area as an initial step. He therefore ordered the 132nd Infantry immediately to seize the objective. While the 132nd Infantry had little modern battle experience aside from jungle skirmishes and patrols, it was proud of its combat history, having participated in both the US Civil War and World War I, and its young reserve officers and non-commissioned officers considered themselves skilled in rifle and machine gun tactics.

The 132nd Infantry’s commander, Colonel Leroy E. Nelson, directed his 3rd Battalion to lead the US assault on the first of several hills, followed by the regiment’s 1st Battalion. Artillery support was provided by 105-mm (4.13-in) howitzers of the 246th Field Artillery Battalion and the 75-mm (2.95-in) pack howitzers of the 2/10th Marines.

The exposed hills constituting the Mt Austen complex were arbitrarily numbered by the Americans for reference purposes. On 17 December, Lieutenant Colonel William C. Wright’s 3rd Battalion advanced south of Hill 35 and began to climb toward Mt Austen’s summit near Hills 20 and 21. In order to adhere to the timetable set by the division, the battalion had to leave behind many of its support weapons, such as heavy mortars and machine guns, and to take only limited quantities of ammunition and supplies, all of which had to be hand-carried along paths hacked through the thick jungle. At 09.30 on 18 December, as Wright’s leading elements approached, Japanese defenders pinned down the US troops with machine gun and rifle fire. Exhausted and dehydrated by their passage through the thick jungle, Wright’s troops were unable to deploy quickly out of column formation and made no headway against the Japanese defences.

During the morning of the next day, after an artillery barrage and attack by aircraft of the Cactus Air Force, Wright went forward with several artillery observers to investigate the terrain in front of his force. A Japanese machine gun team killed Wright with a burst of fire at 09.30. Wright’s second in command, Major Louis Franco, was unable to get forward and take command until a time later in the day, preventing the battalion from continuing the attack. At the same time, Japanese riflemen infiltrated the US positions and effectively harassed the command posts of both the 3rd and 1st Battalions as well as the column of heavily loaded US supply and engineer parties on the jungle trail linking the battalions with the Lunga perimeter. Both US battalions dug in for the night while artillery bombarded the Japanese positions.

Between 20 and 23 December, the Japanese apparently withdrew from the area, as aggressive US Army patrols encountered no more Japanese in the area of Hill 20, Hill 21 and farther to the south. Nelson ordered the two battalions to move westward to Hill 31 and then attack to the south in the direction of Hill 27. On 24 December, the 3rd Battalion was halted on the slopes of Hill 31 by intense machine gun fire from well-concealed positions.

Facing the Americans was the most strongly fortified Japanese position on Guadalcanal, nicknamed by is defenders as 'the Gifu' after Gifu Prefecture in Japan The Gifu position sat between the summits of Mt Austen and Hills 27 and 31 and, and comprised a 1,500-yard (1370-m) line of 45 to 50 interconnected and well-camouflaged pillboxes dug into the ground and forming a horseshoe shape with the open end to the west. Each pillbox extended only about 3 ft (0.9 m) above the ground, and was constructed with walls and a roof of logs and earth up to 2 ft (0.6 m) thick. Each pillbox contained one or two machine guns and several riflemen. Some of the pillboxes were sited below large jungle trees, and each of these pillbox emplacements was sited to provide mutual support to the others. Numerous foxholes and trenches provided additional support and cover for additional riflemen and machine gunners. Behind the pillboxes, the Japanese had positioned 81-mm (3.19-in) and long-range 90-mm (3.54-in) mortars. The Gifu position was commanded by Major Takeyoshi Inagaki with around 800 men of th 2/228th Regiment and the 2/124th Regiment.

Between 25 and 29 December, the Japanese defences prevented the Americans from making any headway in their attempt to overrun the Gifu position. While the US 3rd Battalion, with artillery support, made frontal attacks against the position to pin the defenders, the 1st Battalion attempted to flank the Gifu on the east. As the Japanese defences were fully integrated, however, the flanking attempt failed. By 29 December, the US losses had reached 53 men killed, 129 wounded and 131 taken ill, but morale nonetheless remained high. Assisting the Americans in this battle were Fijian commandos led by officers and non-commissioned officers of the New Zealand Expeditionary Force.

On 2 January, Nelson added Lieutenant Colonel George F. Ferry’s 2nd Battalion to the offensive and sent it on a march around the Gifu position toward Hill 27, and the battalion had reached the lower slopes of the hill by 16.00 without meeting serious resistance. On this same day, physically and mentally exhausted and possibly suffering from malaria, Nelson was replaced as commander of the 132nd Infantry by Lieutenant Colonel Alexander M. George: the sources are unclear whether Nelson requested his own relief or was ordered to relinquish command.

On the next day, elements of the 2/132nd Infantry occupied the summit of Hill 27, surprised and killed a Japanese 75-mm (2.95-in) gun crew, and with help of heavy artillery fire, drove back six Japanese counterattacks. By this time, the soldiers at the top of Hill 27 were running extremely short of ammunition and grenades, with Japanese forces returning 10 shots to each one fired by the Americans, and medical supplies had been exhausted. The 2nd Battalion’s efforts to improve its position were made more difficult by the hard coral underneath the hill’s topsoil, which made the digging of foxholes difficult. The remainder of the 2nd Battalion, carrying ammunition, food and medical supplies, reached Hill 27 and joined the battle, in which it soon gained combat superiority over the attacking Japanese. At the same time, with the infusion of the new leadership of George, the 1st and 3rd Battalions attacked and pushed a short way into the Gifu position, killing 25 Japanese in the process, then closed the gaps between their units and consolidated their positions, while killing many of the Japanese defenders. One 2nd Battalion officer, who had brought his personal sniper rifle to the battle, witnessed the final disintegration of Japanese units attacking Hill 27 in the course of a final spasm of suicidal frontal charges. The Japanese soldiers in the Gifu position, who had apparently not been resupplied or replenished during the battle, ate their last remaining food on 1 January.

Since the beginning of its offensive on Mt Austen, the 132nd Infantry had lost 115 men killed and 272 wounded. The relatively high number of deaths resulted in part from wound infections in the tropical conditions and the impossibility of evacuating wounded men on the early stages of the operation. Even after intervention by the 2nd Battalion, wounded men continued to die, unable to withstand the arduous and slippery portage back down improvised jungle trails on a stretcher carried by two men. These losses, plus the effects of tropical diseases, heat and combat exhaustion, left the 132nd Infantry’s 1st and 3rd Battalions temporarily incapable of further offensive action. Thus, on 4 January, the 1st and 3rd Battalions were ordered to dig in and hold positions surrounding the Gifu on the north, east and south.

While Patch’s decision to attack Mt Austen has been criticised, however, one participant noted the difficulties faced by the 132nd Infantry and its commanders, these difficulties including the terrain, limited equipment (light mortars and machine guns with only the most modest of ammunition supplies, no flamethrowers and no pole charges), and the necessity of assaulting thoroughly integrated, prepared and roofed-over Japanese defences, which resisted direct hits by 75-mm (2.95-in) and in some cases 105-mm (4.13-in) shells.

For its part, once its wounded had started to receive treatment, the newly-blooded 132nd Infantry retained a high level of morale, and this played a significant role in later combat operations on Guadalcanal. The 2nd Battalion, with only 27 men killed, was immediately assigned to further offensive combat operations.

The losses suffered by the Gifu position’s defenders are unknown, but were estimated by one 2nd Battalion officer as 500 men killed and wounded by 9 January; most of the wounded later died from a combination of their injuries with illness and starvation. The diary recovered from one Japanese officer stated that the Japanese had suffered heavy casualties. Japanese prisoners captured in later operations referred to the combat at Hill 27 and Hill 31 as the 'Battle of the Mountain of Blood'.

On 2 January, with the arrival of the US Army’s 25th Division and the rest of the 2nd Marine Division, all of the US units on Guadalcanal and Tulagi were together designated as the XIV Corps with Patch in command. Brigadier General Edmund B. Sebree, up to now Patch’s second in command, now became commander of the Americal Division. On 5 January, Patch issued his plan to begin operations to clear Guadalcanal of Japanese forces. The 2nd Marine Division was to push to the west from the Matanikau river along the coast while the 25th Division was to finish the clearance of Mt Austen and to secure the hill tops and ridges round the inland forks of the Matanikau river. The Americal Division and the 147th Infantry were to protect the Lunga perimeter.

The deep river ravines of the Matanikau river’s upper forks naturally divided the 25th Division’s operational area into three distinct sections, with one main terrain feature dominating each area. To the east of the Matanikau river is Mt Austen; in the wedge between the south-eastern and south-western forks of the Matanikau river, Hills 44 and 43 together form a terrain feature that the Americans called the 'Sea Horse' because of its shape when viewed from above; and between the Matanikau river’s south-western and north-western forks is a much larger hill mass labelled, also because of its shape, as the 'Galloping Horse'.

Commanding the 25th Division, Collins assigned his 35th Infantry to clear the Gifu position, secure the rest of Mt Austen, and capture the Sea Horse. He ordered the 27th Infantry to seize the Galloping Horse from the north. The 35th and 27th Infantry were then to link up on Hill 53 (the ;head' of the Galloping Horse) to finish clearing the nearby hills and ridges. Collins placed his 161st Infantry in reserve. Ammunition and supplies for the attacking troops would be transported by Jeep along rough trails as far forward as possible and then be carried the rest of the way by native Solomon islanders.

Having seen the arrival of the US reinforcements, the Japanese were expecting the US offensive. Hyakutake ordered the units on the hill tops around the Matanikau river and in the Gifu to hold their prepared positions. The Japanese hoped that as the Americans surrounded and intermingled with the Japanese defensive pockets that the inevitable close-quarter fighting would prevent the Americans from employing their superior firepower in artillery and close air support. At night, the Japanese planned to infiltrate the US rear areas and interdict their supply lines to prevent the US assault forces from receiving sufficient ammunition and provisions to continue their attacks. The Japanese hoped to delay the Americans long enough for more reinforcements to arrive from Rabaul or elsewhere.

Viewed from overhead with north upward, the Galloping Horse appears upside down, with Hills 54 and 55 forming the horse’s rear legs and Hill 57 the front legs. From east to west, Hills 50, 51 and 52 formed the horse’s body with the 900-ft (275-m) Hill 53 at the head. Colonel William A. McCulloch, commander of the 27th Regiment,ordered his 1st Battalion to attack Hill 57 and his 3rd Battalion to assault Hills 51 and 52 from Hill 54, which was already in US hands. Defending the Galloping Horse and the nearby fork of the Matanikau river were 600 Japanese of the 3/228th Regiment under the command of Major Haruka Nishiyama.

The US attack got under way at 05.50 on 10 January with a bombardment by six battalions of artillery and attacks by 24 Cactus Air Force aircraft on suspected Japanese positions in the valley between Hill 57 and the 1st Battalion’s jumping-off point. Beginning its advance at 07.30, the 1st Battalion had gained the summit of Hill 57 by 11.40 in the face of only light resistance.

From Hill 54, the 3rd Battalion’s attack route was in the open and dominated by the high ground of Hills 52 and 53. At 06.35, the battalion began its assault and occupied Hill 51 without resistance. Continuing its advance, the battalion was stopped by heavy Japanese machine gun fire 200 yards (185 m) short of Hill 52’s summit. After an attack by six aircraft on Hill 52 and an artillery bombardment, the 3rd Battalion resumed its attack and had captured the summit by 16.25, in the process destroying six machine gun positions and killing about 30 Japanese.

At 09.00 on 11 January, the 3rd Battalion began its attack on Hill 53. The Japanese quickly stopped the US advance with machine gun and mortar fire. Not having received adequate water supplies, the American soldiers began to suffer extensive heat casualties: in one platoon, for example, only 10 men remained conscious by the afternoon.

On the next day, the 27th Infantry’s 2nd Battalion took over the assault on Hill 53. Advancing up the hill, the Americans were stopped short of Hill 53’s summit. During the night, Japanese infiltrators cut the telephone line between the 2nd Battalion and its regimental headquarters, affecting unit communications. On 13 January, the Americans renewed the attack but were again halted by heavy Japanese machine gun and mortar fire.

A knoll on the southern edge of the ridge (the 'horse’s neck') leading to Hill 53 was the key point of the Japanese defence. The knoll contained several machine gun and mortar positions which had effectively held off the US attacks across the ridge. The 2nd Battalion’s executive officer, Captain Charles W. Davis, volunteered to lead four other men against the knoll. Crawling on their bellies, Davis and his party crept to within 10 yd (9 m) of the Japanese position, whose defenders hurled two grenades that failed to explode. Davis and his men threw eight grenades at the Japanese, destroying several of their positions. Davis then stood up, and while shooting his rifle, and then his pistol, with one hand, waved his men forward with the other as he advanced farther onto the knoll. Davis and his men then killed or chased away the rest of the Japanese on the knoll. Silhouetted against the sky during the action, Davis was visible to the Americans all up and down the ridge. Inspired by his actions, and refreshed by a sudden thunderstorm, the US troops were revived and quickly assaulted Hill 53, which had been taken by 12.00. The Americans counted the bodies of 170 Japanese soldiers on and around the Galloping Horse, and had themselves suffered fewer than 100 killed.

Between 15 and 22 January, the 161st Infantry hunted the remainder of Nishiyama’s battalion in the nearby gorge of the south-western fork of the Matanikau river. In total, 400 Japanese were killed defending the Galloping Horse and surrounding area, and 200 Japanese survivors, including Nishiyama, escaped to the west on 19 January.

The 35th Infantry, commanded by Colonel Robert B. McClure, had been assigned to capture the Sea Horse and complete the reduction of the Gifu position on Mt Austen. McClure assigned his 2nd Battalion to the assault on the Gifu and sent his 1st and 3rd Battalions on a long march through the jungle to attack the Sea Horse from the south. Defending the Sea Horse and nearby valleys were the 124th Regiment's 1st and 3rd Battalions, with Oka’s command post located nearby. The Sea Horse consisted of two hills, Hill 43 on the south and the adjacent Hill 44 on the north.

After its 7,000-yard (6400-m) circuitous route through the jungle around Mt Austen, at 06.35 on 10 January McClure’s 3rd Battalion launched its attack on Hill 43. As the Americans closed on the hill from the south, a party of Japanese soldiers near Oka’s command post spotted them as they crossed a stream and immediately attacked, threatening the flank of the US column. Two US soldiers repelled the Japanese attack with a machine gun but were killed in the process. Making progress against light resistance, the 3rd Battalion dug in for the night about 700 yards (640 m) short of Hill 43’s summit.

One the following day, the 1/35th Infantry was added to the attack and with artillery support the two battalions drove through several Japanese machine gun positions and had taken Hill 43 by a time early in the afternoon. Continuing toward Hill 44 against light opposition, the Americans had captured the rest of the Sea Horse by the fall of night and there by cutting off Japanese forces in the Gifu position. The native Solomon islanders who had been man-packing supplies to the two US battalions during the attack were having difficulty delivering sufficient food and ammunition over the long trail between the Sea Horse and the Lunga perimeter, so Boeing B-17 Flying Fortress heavy bombers were now used to air drop supplies to the US troops around the Sea Horse.

On 12 January, the two battalions of the 35th Infantry continued their attack to the west in the direction of the Galloping Horse, but were stopped by a Japanese strongpoint on a narrow ridge about 600 yards (550 m) to the west of their point of departure. After trying to flank the position for two days, the Americans were able to destroy the strongpoint with mortar and artillery fire, killing 13 defenders, and had advanced to a ridge overlooking the south-western fork of the Matanikau river by 15:00 on 15 January. During that same day, the Japanese survivors from the Sea Horse battle, including Oka and most of the 124th Regiment's headquarters staff section and the 1/124th Regiment, were able to slip past the US forces and reach a temporary refuge farther to the west. The Americans counted 558 Japanese dead around the Sea Horse, mostly from the 3/124th Regiment, and captured 17 men.

On 9 January, Lieutenant Colonel Ernest Peters’s 2nd Battalion replaced the three battalions of the 132nd Infantry and prepared to assault the Gifu. Over the next four days, the Americans tried to establish the locations and strengths of the Japanese positions with patrols. At the same time, the Gifu’s defenders attempted to wear down the Americans with night infiltration attacks, and by 13 January the 2nd Battalion had lost 57 men killed or wounded. The battle casualties combined with malaria to reduce the battalion to three-quarters of its nominal strength by the next day. To assist the battalion, the personnel of the 35th Infantry’s anti-tank gun company were attached to the battalion as infantry.

With the capture of the Sea Horse feature by the Americans, the Japanese in the Gifu were now isolated from the rest of the 17th Army. In a last message over his field telephone before the line was cut, Inagaki refused an order from Oka to abandon his position and attempt to infiltrate back to friendly lines, instead vowing that his command would fight to the last. Inagaki apparently refused the order because to do so would have meant the abandonment of his sick and injured men.

A US attack on the Gifu by the whole 2nd Battalion on 15 January was completely repulsed by the Japanese. On 16 January McClure replaced Peters with Major Stanley R. Larsen, who decided to effect a complete encirclement of the Gifu and attempt to reduce it with a massive artillery bombardment on 17 January.

In the meantime, the Americans used a loudspeaker to broadcast a surrender appeal in Japanese to the Gifu’s defenders. Only five Japanese soldiers responded. One of the five reported that his company actually gathered to discuss the appeal, but decided not to surrender because they were too weak to carry their injured comrades who could not walk to the US lines. Instead, they elected to die together as a unit. One Japanese officer defending the Gifu wrote in his diary that 'I heard the enemy talking in Japanese over a loudspeaker. He is probably telling us to come out – what fools the enemy are. The Japanese army will stick it out to the end. Position must be defended in all conditions with our lives.'

At 14.30 on 17 January, 12 155-mm (6.1-in) and 37 105-mm (4.13-in) guns opened fire on the Gifu. Over the following 90 minutes, the US artillery fired 1,700 shells into an area about 1,000 yd (915 m) square. As it was late in the day, the Americans not not follow the barrage with an immediate attack, but instead waited to the following day, and this made it possible for the Japanese to recover. On 18 January, the Americans attacked into the weaker western side of the Gifu, making some headway and destroying several Japanese pillboxes over the next two days until heavy rain stopped the attack on 20 January. During that night, 11 Japanese were killed while trying to escape from the Gifu.

On 22 January, the Americans were able to move a light tank along their supply trail to Mt Austen, and this vehicle proved to be the decisive factor in the battle. At 10.20 the tank, which was protected by between 16 and 18 infantrymen, destroyed three Japanese pillboxes and penetrated into the Gifu pocket. Pressing forward, the tank crossed the Gifu position and destroyed five more pillboxes, opening a gap 200 yards (185 m) wide in the Japanese line. The US infantry surged through the gap and took positions in the middle of the Gifu.

At about 02.30, apparently realising that the battle was now lost, Inagaki led his staff and most of the remaining 100 or so survivors of his command in a final charge. Inagaki and the remainder of his men were killed almost to the last man. As the sun rose on 23 January, the Americans secured the rest of the Gifu. Some 64 men of the 2/35th Infantry were killed during the assaults on the Gifu between 9 and 23 January, bringing the total number of US dead in the taking of Mt Austen to 175. The Americans counted the bodies of 431 Japanese in the remains of the Gifu’s fortifications and 87 elsewhere around Mt Austen. The total Japanese losses in the Sea Horse and both Mt Austen battles were probably between 1,100 and 1,500 men.

During the time of the US Army offensive in the hills around the upper reaches of the Matanikau river, the 2nd Marine Division, under the command of Brigadier General Alphonse DeCarre, was attacking to the west along the northern coast of Guadalcanal. Facing the marines in the hills and ravines to the south of Point Cruz were the remnants of Maruyama’s 2nd Division, plus the 1/228th Regiment of the 38th Division under the command of Major Kikuo Hayakawa.

On 13 January, the 2nd and 8th Marines began their offensive with the 8th Marines attacking along the coast and the 2nd Marines advancing farther inland. The Japanese were pushed back in some places but held in others, and there was heavy fighting at several places in the hills and ravines near the coast. On 14 January, the 2nd Marines were relieved by the 6th Marines under the command of Colonel Gilder D. Jackson. The Marines renewed their offensive on 15 January. The Japanese checked the 8th Marines' advance along the coast, but inland the 6th Marines were able to advance about 1,500 yards (1370 m) and threatened the flank of the Japanese forces emplaced in front of the 8th Marines. At 17.00, Maruyama ordered his troops to retreat to a pre-ordained line about 1,300 yards (1190 m) to the west. Early on 16 January, as many of Maruyama’s men attempted to comply with the order to retreat, the 6th Marines turned and drove to the coast, trapping most of Maruyama’s 4th Regiment and 16th Regiment between themselves and the 8th Marines. By 14.00 on 17 January, the marines had destroyed the Japanese forces trapped in the pocket, killing 643 men and taking prisoner just two.

On 15 January, a representative of the Imperial Japanese army from Rabaul reached Guadalcanal in the course of a 'Tokyo Express' mission and informed Hyakutake of the decision to withdraw the surviving Japanese forces from the island. Grudgingly accepting the order, the 17th Army's staff communicated the 'Ke' (i) evacuation plan to the army’s surviving forces on 18 January. The plan directed the 38th Division to disengage and withdraw towards Cape Esperance on the western end of Guadalcanal beginning on 20 January. The 38th Division's retirement was to be covered by the 2nd Division and other units, which would then follow the 38th Division to the west. Any troops unable to move were encouraged to kill themselves to 'uphold the honor of the Imperial Army'. From Cape Esperance the Japanese navy planned to evacuate the army forces over the last few days of January and first week of February with a projected completion date of 10 February.

The US forces and their allies mistook Japanese preparations for 'Ke' (i) as another reinforcement attempt. With this in mind, Patch ordered his forces to launch another offensive against the Japanese forces to the west of the Matanikau river. On 21 January, the 27th and 161st Regiments pushed westward from the area of the Galloping Horse. Unaware of the fact that the 38th Division was withdrawing in preparation to evacuate the island, the US forces were surprised to encounter only light resistance. Advancing more quickly through the inland hills and ridges than the Japanese had anticipated, by 22 January the Americans were in position to capture Kokumbona, headquarters of the 17th Army on the coast and cut off the remainder of the 2nd Division.

Reacting quickly to the situation, the Japanese hurriedly evacuated Kokumbona and ordered the 2nd Division immediately to retire to the west. The Americans captured Kokumbona on 23 January. Although some Japanese units were trapped between the converging US forces and destroyed, most of the 2nd Division's survivors escaped. In the course of the following week, the Japanese rearguard, assisted by difficult terrain, effectively delayed the US advance to the west from Kokumbona. Still believing that a Japanese reinforcement effort was imminent, Patch kept most of his forces back to guard Henderson Field, sending only one regiment at a time to continue the advance. The majority of the surviving Japanese forces were therefore able to gather at Cape Esperance by the end of January. On 1, 4, and 7 February, Japanese warships successfully evacuated 10,652 men from the island. On 9 February, the Americans discovered that the Japanese were gone and declared Guadalcanal secure.

With hindsight, some have faulted the Americans, and especially Patch and Admiral William F. Halsey, the latter commanding the Allied forces in the South Pacific Area, for not taking advantage of their land, air and sea superiority to prevent the Japanese evacuation of most of their surviving forces from Guadalcanal. Just recently, Halsey had been repulsed in the 'Battle of Rennell Island'. Patch and Harmon’s insistence on taking Mt Austen has been cited as one of the factors that delayed the US main attack to the west, providing the 17th Army with the opportunity to escape.

Nevertheless, the success of the overall campaign to take Guadalcanal from the Japanese was an important strategic victory for the USA and its allies. Building on their success at Guadalcanal and elsewhere, the Allies were thus well sited to continue their campaign against Japan, ultimately culminating in Japan’s defeat and the end of World War II.