When was the Battle of the Tenaru?

It was fought on 21 August 1942 on Guadalcanal, from the Japanese night attack at about 03:10 until the last resistance ended at 17:00.

Why is it called the Tenaru if it was fought on another river?

The Marines' maps misnamed the stream. The fighting was at the mouth of the Ilu, also called Alligator Creek, but the battle kept the name Tenaru.

How many men did Colonel Ichiki have?

His forward echelon that landed at Taivu Point numbered about 900 men. The rest of his unit was to follow later.

What were the losses at the Tenaru?

The Marine Corps histories give nearly 800 Japanese killed and 15 captured, and 34 Marines killed and 75 wounded.

A sergeant major of the Solomon Islands constabulary who was captured and tortured by the Japanese, refused to talk, escaped and warned the Marines of the coming attack.

Battle of the Tenaru, 1942: the first attack on Guadalcanal

The Bloody Angle at the river mouth, seen from the Marine lines, Guadalcanal, 1942. Official USMC photograph, USMC History Division Archives, via Wikimedia Commons, CC BY 2.0.

Quick answer

What was the Battle of the Tenaru?

It was the first Japanese ground attack against the US Marine beachhead on Guadalcanal. In the early hours of 21 August 1942, about 900 men under Colonel Kiyono Ichiki charged across a sandspit at the mouth of the Ilu River, then believed to be the Tenaru. Marine rifle, machine-gun and canister fire broke the attack, a Marine battalion encircled the survivors and tanks finished them off by 17:00. Nearly the whole Japanese force was killed.¹

On 7 August 1942 the 1st Marine Division landed on Guadalcanal in the Solomon Islands and took the airfield the Japanese were building at Lunga Point, soon named Henderson Field. Within two days the Allied ships had left, and the Marines were alone with short supplies and little intelligence about the enemy on the island. General Alexander Vandegrift drew his small force into a perimeter around the airfield, with the strongest positions on the beach against a landing from the sea.²

Ichiki's detachment

The Marine landing upset Japanese plans in the South Pacific. The first sizable reinforcement sent to retake the airfield was the reinforced 2nd Battalion of the 28th Infantry under Colonel Kiyono Ichiki. The unit had been meant for the occupation of Midway and was on its way home when it was diverted to Truk, where it arrived on 12 August. Six destroyers carried its forward echelon, about 900 men by the Marine Corps monograph, to Taivu Point, some 22 air miles east of the Lunga, where it landed during the night of 18 August.³

The next day a Marine patrol under Captain Brush ran into Ichiki's reconnaissance party and wiped it out. According to the official History of US Marine Corps Operations in World War II, Ichiki, shaken at being discovered, decided to attack at once. Vandegrift had five infantry battalions and could not be sure that this was the main enemy landing, so he kept his reserve inside the perimeter and waited.⁴

Vouza's warning

During the night of 20 to 21 August, Marine listening posts east of the river heard troops moving through the jungle and fell back to the lines of Lieutenant Colonel Edwin Pollock's 2nd Battalion, 1st Marines, which held the river mouth. At about the same time Sergeant Major Jacob Vouza of the Solomon Islands constabulary staggered into Pollock's command post. Caught by the Japanese in his village, he had refused to talk, been bayoneted and left for dead, and had made his way through the enemy force to warn the Marines.⁵

The river was not the Tenaru at all. It was the Ilu, also called Alligator Creek, which the Marines' maps of the time misnamed, and the battle kept the wrong name.⁶

The charge across the sandspit

At 03:10 on 21 August a column of about 200 Japanese rushed the sandspit at the river mouth. Rifle and machine-gun fire and a 37mm gun firing canister cut most of them down, but the position was not wired in, and a few broke into the Marine line and took some emplacements. Company G, the battalion reserve, counterattacked and cleared them out. Ichiki then shelled the Marine positions with mortars and 70mm guns and sent a second company wading out beyond the breakers to come ashore west of the river mouth. It was shattered at the water's edge by machine guns, canister and the 75mm pack howitzers of the 11th Marines.⁷

Encirclement

At daybreak Pollock reported that he could hold. The bend of the river let part of his line fire along the Japanese position, and his artillery support was strong. Vandegrift ordered the division reserve, Lieutenant Colonel Lenard Cresswell's 1st Battalion, 1st Marines, to cross the river upstream and attack the Japanese from the left and rear. By 14:00 the enemy was penned in between the river, the beach and Cresswell's companies. Attempts to break out along the beach or through the surf failed, and the fighter pilots of VMF-223, on the island less than a day, strafed the Japanese for the first time.⁸

To finish the fight before dark, Vandegrift sent a platoon of light tanks across the sandspit at 15:00. One was lost to a mine, but the attack rolled through the Japanese positions. By 17:00 it was over.⁹

The toll

The Marine Corps histories agree on the cost: nearly 800 Japanese killed and 15 taken prisoner, with only a few escaping into the jungle, against 34 Marines killed and 75 wounded. Ichiki, in the words of the official history, committed suicide, disgraced by the debacle. Admiral Raizo Tanaka, who had carried his men to the island, later wrote that the episode showed infantry with rifles and bayonets had no chance against an enemy with modern heavy weapons.¹⁰

The battle was a small one by the standards of the Pacific war, but it was the first time the Japanese army tried to retake Guadalcanal on land and failed. It set the pattern of the campaign: Japanese units landed piecemeal and thrown against a defended perimeter, and Marine firepower holding the airfield on which everything depended. The second echelon of Ichiki's force never got ashore in strength, as the naval Battle of the Eastern Solomons turned it back three days later.¹¹ › Carlson's Long Patrol, 1942

Notes

A number in the text points to a note; each note names the works that paragraph draws on, listed in full under Sources.

John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
Frank O. Hough, “Part VI, Chapter 4”; John L. Zimmerman, “Chapter IV”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩
John L. Zimmerman, “Chapter IV”; Frank O. Hough, “Part VI, Chapter 4”. ↩

Sources

John L. Zimmerman, The Guadalcanal Campaign, USMC Historical Monograph (1949), via HyperWar, “Chapter IV: Establishment of the Perimeter and Battle of the Tenaru”
Frank O. Hough, Verle E. Ludwig and Henry I. Shaw, History of US Marine Corps Operations in World War II, Vol. I (1958), via HyperWar, “Part VI, Chapter 4: The Battle of the Tenaru”