Actions Along The Matanikau - Background

Background

On 7 August 1942, Allied forces (primarily American) landed on Guadalcanal, Tulagi, and Florida Islands in the Solomon Islands. The landings on the islands were meant to deny their use by the Japanese as bases for threatening the supply routes between the U.S. and Australia, and secure the islands as starting points for a campaign with the eventual goal of neutralizing the major Japanese base at Rabaul while also supporting the Allied New Guinea campaign. The landings initiated the six-month-long Guadalcanal campaign. Taking the Japanese by surprise, by nightfall on 8 August the Allied landing forces had secured Tulagi and nearby small islands, as well as an airfield, later called Henderson Field by Allied forces, under construction at Lunga Point on Guadalcanal.

In response to the Allied landings on Guadalcanal, the Japanese Imperial General Headquarters assigned the Imperial Japanese Army's 17th Army—a corps-sized command based at Rabaul and under the command of Lieutenant-General Harukichi Hyakutake—with the task of retaking Guadalcanal from Allied forces. The 17th Army—currently heavily involved with the Japanese campaign in New Guinea—had only a few units available to send to the southern Solomons area. Of these units, the 35th Infantry Brigade under Major General Kiyotake Kawaguchi was at Palau, the 4th (Aoba) Infantry Regiment was in the Philippines and the 28th (Ichiki) Infantry Regiment was embarked on transport ships near Guam. The different units began to move towards Guadalcanal immediately, but Ichiki's regiment—being the closest—arrived first. The "First Element" of Ichiki's unit—consisting of about 917 soldiers—landed from destroyers at Taivu Point, east of the Lunga perimeter, on 19 August, attacked the U.S. Marine defenses, and were almost completely annihilated during the resulting Battle of the Tenaru on August 21.

Between 29 August and 7 September, Japanese destroyers (called "Tokyo Express" by Allied forces), plus a convoy of slow barges, delivered the 6,000 men of Kawaguchi's brigade, including the rest of Ichiki's regiment (called the Kuma Battalion) and much of the Aoba regiment, to Guadalcanal. General Kawaguchi and 5,000 of the troops landed 20 mi (32 km) east of the Lunga Perimeter at Taivu Point. The other 1,000 troops—under the command of Colonel Akinosuka Oka—landed west of the Lunga Perimeter at Kokumbona. During this time, Vandegrift continued to direct efforts to strengthen and improve the defenses of the Lunga perimeter. Between 21 August and 3 September, he relocated three Marine battalions—including the 1st Raider Battalion, under U.S. Lieutenant Colonel Merritt A. Edson (Edson's Raiders)—from Tulagi and Gavutu to Guadalcanal.

Kawaguchi's Center Body of 3,000 troops began their attacks on a ridge south of Henderson Field beginning on 12 September in what was later called the Battle of Edson's Ridge. After numerous frontal assaults, Kawaguchi's attack was repulsed with heavy losses for the Japanese, who retreated back into the jungle on 14 September. Oka's assault in the west and the Kuma Battalion's assault in the east were also repulsed by the U.S. Marines over the same two days. Kawaguchi's units were ordered to withdraw west to the Matanikau Valley to join with Oka's unit on the west side of the Lunga Perimeter. Most of Kawaguchi's men reached the Matanikau by 20 September.

As the Japanese regrouped west of the Matanikau, the U.S. forces concentrated on shoring up and strengthening their Lunga defenses. On 18 September, an Allied naval convoy delivered 4,157 men from the 3rd Provisional Marine Brigade (U.S. 7th Marine Regiment) to Guadalcanal. These reinforcements allowed Vandegrift—beginning on 19 September—to establish an unbroken line of defense completely around the Lunga perimeter.

The Japanese immediately 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, too late to join Kawaguchi's attack on the U.S. Marines. By then, though, the battalion had joined Oka's forces near the Matanikau. Subsequent Tokyo Express runs—beginning on 15 September—brought food and ammunition—as well as 280 men from the 1st Battalion, Aoba Regiment—to Kamimbo on Guadalcanal.

U.S. Marine Lieutenant General Vandegrift and his staff were aware that Kawaguchi's troops had retreated to the area west of the Matanikau and that numerous groups of Japanese stragglers were scattered throughout the area between the Lunga Perimeter and the Matanikau River. Two previous raids by Marines—on 19 and 29 August—had killed some of the Japanese forces camped in that area but had failed to deny the location as an assembly area and defensive position for the Japanese forces threatening the western portion of the Marine defenses. Vandegrift, therefore, decided to conduct another series of small unit operations around the Matanikau Valley. The purpose of these operations was to "mop-up" the scattered groups of Japanese troops east of the Matanikau and to keep the main body of Japanese soldiers off-balance to prevent them from consolidating their positions so close to the main Marine defenses at Lunga Point. The first operation was assigned to the 1st Battalion, 7th Marine Regiment under Lieutenant Colonel Chesty Puller with a start date of 23 September. The operation would be supported by artillery fire from the U.S. 11th Marine Regiment.