Operation Watchtower: The US invasion of Guadalcanal begins

The first months of World War II went very badly for the Americans. The Japanese had caught the Pacific Fleet in Pearl Harbor flatfooted and at anchor and had put a massive blow on American naval power. 

After that, the Japanese had made lightning assaults and had easily taken the Philippines, Wake Island, Guam, Thailand, Malaya, Singapore, the Dutch East Indies, New Britain, the Gilbert Islands, Rabaul, Hong Kong. They were moving to Burma, New Guinea, and reaching deeper into China. It was victory after victory and the Japanese Empire seemed unstoppable. But it all began to change. 

Admiral Isoroku Yamamoto, the architect of Pearl Harbor and the head of the Japanese Fleet, made a statement that turned out to be quite prophetic.

“In the first six months of a war with the United States, I will run wild and win victory upon victory. But then, if the war continues after that, I make no such guarantees.”

In April of 1942, the United States conducted the Doolittle Raid, by launching land-based B-25 bombers off of an aircraft carrier. In May, a Japanese invasion fleet headed for Port Moresby was stopped at the Battle of the Coral Sea. While technically the Battle of Coral Sea was a draw, the Japanese fleet retreated. But in Yamamoto’s daring and intricate plan to once and for all destroy the U.S. Pacific fleet with the invasion of Midway, the Japanese had suffered a crushing defeat… and six months to the day from the attack on Pearl Harbor. 

In August, against the island of Guadalcanal, the United States would be making its first offensive amphibious operation of the war in the Pacific. It would be called “Operation Watchtower” and set the stage for many to come. Yet, the Guadalcanal invasion, compared to what would follow, was a comparable shoestring operation. In July of 1942, the Japanese moved into the Solomon Islands and occupied Tulagi and Guadalcanal, where they began construction on an airfield. With that, they could threaten any American fleet coming to aid a move on Port Moresby. 

The U.S. Joint Chiefs of Staff were in disagreement of which way to go due to service in-fighting. They finally settled on Guadalcanal and made it a point to stress that seizure of the airfield was imperative. Due to bad weather, the U.S. Marines under Major General Alexander A Vandegrift of the 1st Marine Division landed on Guadalcanal, Tulagi, and Florida Island nearly undetected on the night of August 6-7, 1942. The Japanese troops on Tulagi and Florida Island put up fierce resistance but were wiped out to the man by the 9th. 

The Marines at Guadalcanal landed unopposed and were quickly able to seize the all-important airfield renaming it Henderson Field. The Japanese troops at the airfield panicked during the naval bombardment and abandoned everything at the uncompleted airstrip, including food, supplies, all-important construction equipment, and vehicles.

Admiral Frank Fletcher was worried about Japanese air attacks and his fuel supply and withdrew the carriers from the Solomons on the night of August 8. Admiral Richmond Turner, with no air cover, withdrew the remainder of the Navy ships, leaving with much of the Marines’ supplies and nearly all of their heavy equipment. He planned on returning on the evening of the 9th, but his screening force of cruisers and destroyers was surprised and routed by a Japanese force. The Japanese were experts at night fighting at sea. 

However, Japanese Vice Admiral Gunichi Mikawa, not knowing the carriers were gone, worried about getting caught during daylight by air attacks and withdrew to Rabaul, without attacking the transports which were still full of Marines. It was an understandable but critical mistake, one of several the Japanese would make. With Turner withdrawing again, the 11,000 Marines were, for a time, on their own. 

The Marines, using captured Japanese heavy equipment, had Henderson Airfield open by August 18. By the 20th, the escort carrier USS Long Island delivered 19 F4F Wildcat fighters and 12 SBD Dauntless dive bombers. Soon after, five U.S. Army P400 Airacobras arrived. Thus began the “Cactus Air Force” as the flyers were called. 

On the 21st, the Japanese landed a regiment of 917 infantrymen and forced marched 9 miles to the Marines’ position. In a case of arrogance, over-confidence, and underestimating the strength of the enemy, they launched into a frontal assault without reconnoitering. The Marines decimated them during the night and then counterattacked the next day killing 789 of them including the regiment’s commander. 

The Japanese sortied a fleet with three carriers: the two fleet carriers Shōkaku and Zuikaku, and the light carrier Ryūjō. The Americans had two carriers in the area, the Enterprise, and Saratoga. The Japanese used the Ryūjō as bait to lure Fletcher’s carriers out. The smaller Japanese carrier was hit by multiple 1,000-lb bombs and an aerial-launched torpedo. She was a flaming wreck and sank later that night. Enterprise was damaged and would need months of repairs. Both carrier forces withdrew. 

The transports from the Japanese fleet were attacked by the Cactus Air Force. One was sunk and the Japanese withdrew and transferred the remainder of the troops to destroyers to attempt landings later. The Enterprise shuttled aircraft to Guadalcanal. That was a strategic victory for the Americans. The Cactus Air Force attacked anything that attempted to land and the Japanese were forced to attempt resupply missions only during the hours of darkness. 

Small American convoys arrived between late August and early September. They were able to bring in food, supplies, ammunition, aircraft fuel, and nearly 400 Seabees who immediately went about improving Henderson Field which now boasted 64 aircraft. 

The Japanese during the same timeframe were bringing in some 5,000 troops by landing them in destroyers at night, rather than in slow transports which could come under air attacks. They planned a large three-pronged attack designed to annihilate the Marines and left behind a small force of 250 men to guard their supply base at Taivu. 

Marine Raiders commanded by LTC Merritt Edson landed by boat behind them. They drove the Japanese defenders into the jungle and destroyed nearly everything in the supply base while confiscating intelligence that nailed down the Japanese plan of attack. 

The Japanese attacked along a ridgeline with 3,000 troops against Edson’s 830 men. The fighting was fierce, with hand-to-hand combat during the night of September 12. Wave after wave of frontal assaults was beaten back. By the time Japanese general Kawaguchi withdrew his shattered brigade, he had lost 850 men. The Marines lost 104, but they held. They dubbed the battle “Edson’s Ridge.”

With both sides bringing in reinforcements, the Japanese landed an additional 15,000 troops. They were preparing another large counterattack against Henderson Field. The Americans were bringing in fresh Army troops from the Americal Division. Japanese intelligence told their commanders that there 10,000 American troops on the island, when in fact there were over 23,000. 

On October 24, once again, the Japanese came at the Marines from the south and attacked the Lunga perimeter using numerous frontal assaults. Marines and Army infantry ripped into the waves of attacking infantry. In the carnage around the battle, the Americans killed over 2,200-3,000 of the enemy while only losing 80 troops of their own. The Japanese retreated.

On the 26th of October, the Battle of the Santa Cruz Islands resulted in the loss of the American carrier Hornet, with the Enterprise heavily damaged. The Japanese had two of their carriers heavily damaged. And although the Americans withdrew, it was a Pyrrhic victory for Japan as it lost too many aircraft and trained aircrews that could not be replaced. 

The Japanese troops on Guadalcanal were being pushed back everywhere by aggressive American troops. The Japanese were made to believe that the American troops were soft and would not fight decisively. The Japanese were also sick with tropical diseases and were starving. 

Naval forces continued to inflict heavy losses on one another to the extent that the troops called the waters off Guadalcanal “Ironbottom Sound.” On the 13th of November, Japanese cruisers heavily damaged a U.S. Task Force, sinking several cruisers and a destroyer. But the next day, Cactus Air Force aircraft decimated the transports trying to shuttle troops into the island, sinking seven, and a heavy cruiser. 

The Japanese attempted to beach four more transports at Tassafaronga late in the evening and tried to offload all of the troops and supplies before daylight. But they were spotted at 05:55 and were attacked by air. All four of the transports were destroyed and only about 3,000 troops were offloaded. Most of the supplies never made it to the troops. The planned operation to retake Henderson Field was canceled. 

American air attacks were wreaking havoc on the Japanese during daylight hours. The Japanese resupplying efforts were increasingly unable to keep up with the demand. Some troops were on ⅓ rations. By mid-December, the Japanese had decided to withdraw from Guadalcanal. 

In early January the Americans launched a major attack on an area called Mount Austen and two adjoining ridges called the Seahorse and the Galloping Horse. After some fierce fighting, they broke through and routed the Japanese killing over 3,100 while losing some 250 of their own. 

On the nights of February 4 and 7, the Japanese were able to withdraw all of their remaining forces from Guadalcanal. The next day, Army General Patch, who had assumed command after many of the Marines were relieved in December, announced that the island was secure. 

The Japanese were defeated for the first time on land. The Allies, in just 14 months after Pearl Harbor, had gained the initiative and would not lose it until the war’s end. It was the last time the Japanese would be on the offensive in the Pacific. 

In April 1943, Yamamoto went on a tour of the Japanese forward area around Rabaul. Some of his own staff discouraged the trip, but others did not believe that the Americans had any aircraft capable of making that long of a flight. Once again, they were wrong. 

Army long-range P-38 fighters with extra belly tanks, flying out of Henderson Field were able to intercept Yamamoto, thanks to intelligence personnel breaking the Japanese codes. Yamamoto’s “Betty” bomber was shot down and the architect of Pearl Harbor was dead. His loss definitely shortened the war. 

“Guadalcanal is no longer merely a name of an island in Japanese military history. It is the name of the graveyard of the Japanese army.”

—Major General Kiyotake Kawaguchi, IJA

Commander, 35th Infantry Brigade at Guadalcanal