Operation Watchtower, Capture of the Tulagi and Gavutu–Tanambogo Islands

Operation

In May 1942, U.S. Marine Major General Alexander Vandegrift received orders to move his 1^st Marine Division from the United States to New Zealand as part of the preparations for the Pacific offensive. Allied forces also establish or reinforce bases in Fiji, Samoa, New Hebrides, and New Caledonia. Espiritu Santo in the New Hebrides is chosen as the headquarters and main base for the offensive, codenamed Operation Watchtower, set to commence on August 7^th, 1942.

Initially, the Allied offensive focuses on Tulagi and the Santa Cruz Islands, with Guadalcanal omitted from the plan. However, upon discovering Japanese airfield construction efforts on Guadalcanal, its capture is added to the plan, leading to the exclusion of the Santa Cruz operation. Despite the large-scale movement of Allied forces being detected by Japanese signals intelligence, the Japanese believe the Allies are reinforcing Australia or possibly Port Moresby in New Guinea.

The Watchtower force, consisting of 75 warships and transports from the United States and Australia, assembles near Fiji on 26 July and conducts one rehearsal landing before departing for Guadalcanal on July 31^st, 1942. U.S. Vice Admiral Frank Fletcher commands the Allied expeditionary force (Task Force 61), with his flag onboard of the aircraft carrier U.S.S. Saratoga. Rear Admiral Richmond K. Turner commands the amphibious forces. Vandegrift leads the 16,000-strong Allied landing forces, primarily U.S. Marines.

The troops that are sent to Guadalcanal are freshly trained and equipped with bolt-action M 1903 Springfield rifles, with only a meager 10-day supply of ammunition due to the urgency of getting them into battle quickly. The operation planners reduce their supplies from 90 to 60 days, leading the men of the 1^st Marine Division to nickname the upcoming battle “Operation Shoestring”.

General Vandegrift, commanding the 1^st Marine Division, strategised the Guadalcanal assault, dividing his forces into two groups. One group, led by Vandegrift, executes the main landings at Lunga Point, while the other, under Brigadier General William H. Rupertus, lands across the Sealark Channel in the Florida Island group. Rupertus’ contingent includes the 1^st Raider Battalion under Lieutenant Colonel Edson, the 1^st Provisional Battalion under Major Robert H. Williams, and the 2^nd Battalion, 5^th Marines under Lieutenant Colonel Harold E. Rosecrans.

Islands

Tulagi, an island nestled in Gavutu Harbor and formed by the irregular southern coast of Florida Island, boasts a long, narrow, hilly terrain covered in dense vegetation. It spans approximately 3,7 kilometres in length and 900 metres in width, with its axis running northwest to southeast. The island’s northern two-thirds are dominated by a wooded spine rising 100 metres high, while a lesser ridge sits at the southeastern end, separated from the larger ridge by a saddle depression. Tulagi is currently the administrative centre of the British Solomon Islands Government, with development concentrated around the southeastern tip and the saddle area. The island is defended by a little more than 900 men of the 3^rd Kure Special Naval Landing Force.

The neighbouring islets of Gavutu and Tanambogo serve as a Japanese seaplane base, accommodating 536 Japanese naval personnel from the Yokohama Air Group under the command of Captain Shigetoshi Miyazaki and 3^rd Kure Special Naval Landing Force, alongside Korean and Japanese civilian technicians and labourers from the 14^th Construction Unit.

These two islets consist essentially of coral mounds, both approximately 42 metres high, interconnected by a 500-metre causeway. Termed Hills 148 and 121 respectively by the Americans due to their elevation in feet, the hills on Gavutu and Tanambogo are heavily fortified by the Japanese with bunkers and caves constructed both on and within the two hills. Furthermore, the strategic positioning of the islets allows for mutual support, as each is within machine gun range of the other.

August 7th, 1942

Poor weather conditions provide cover for the Allied expeditionary force, allowing them to approach Guadalcanal undetected by the Japanese on the morning of August 7^th, 1942. However, the Japanese intercept radio transmissions from the incoming Allied invasion force and prepare to deploy scout aircraft at daybreak. The landing force divides into two groups, with one assigned to the assault on Guadalcanal and the other tasked with attacking Tulagi, Florida, and Gavutu-Tanambogo.

Aircraft from the U.S.S. Wasp aircraft carrier conduct dive-bombing raids on Japanese installations on Tulagi, Gavutu, Tanambogo, and Florida. They also strafe and destroy 15 Japanese seaplanes floating in the anchorages near the islands. Some of these seaplanes were in the process of warming their engines for takeoff, resulting in the loss of aircrews and support personnel.

The Cruiser U.S.S. San Juan and Destroyers U.S.S. Monssen and U.S.S. Buchanan shell planned landing sites on Tulagi and Florida Island. Meanwhile, to support the assaults on Tulagi, Gavutu, and Tanambogo, U.S. Marines from the 1^st Battalion, 2nd Marine Regiment land unopposed on Florida Island at 07:40. They receive guidance to their objective from several Australians, including Lieutenant Frank Stackpool, who have previous experience living and working in the Tulagi-Florida area.

The initial landing on Tulagi takes place at 08:00, spearheaded by Companies B and D of the 1^st Raider Battalion commanded by Colonel Merritt A. Edson, also known as Edson’s Raiders, near the western tip.

The presence of coral beds near the shore prevents the landing craft from reaching the shoreline. Nevertheless, the Marines manage to wade the remaining 100 meters in water up to armpit depth. The Japanese are caught off guard by the landings and have not yet initiated any organised resistance. Following the successful landing of Companies B and D, Companies A, C, and E follow suit. The raiders are followed by 2^nd Battalion, 5^th Marines led by Lieutenant Colonel Harold E. Rosecrans.

The Japanese defenders communicate with their commander at Rabaul, Rear Admiral Sadayoshi Yamada. They report that they are under attack and start to begin destroying their equipment and documents. They conclude their message with the statement, “Enemy troop strength is overwhelming, We will defend to the last man.” In response, Masaaki Suzuki, the commander of the SNLF unit, instructs his troops to take up defensive positions that have previously been prepared on Tulagi and Gavutu.

After securing the native village of Sasapi, the Raider Battalion forms a line across the ridge. Company B extends from the northern coastline to halfway up the ridge, connecting with the left flank of Company D, which extends to the crest. On the southern slopes, Company A positions itself, with its right flank connecting with Company C, forming the line down to the southern coastline. Company E, equipped with 60 millimeter mortars, provides beach security near the landing area.

The Marines from the 2^nd Battalion, 5^th Marines, successfully secure the northwest end of Tulagi without encountering any opposition. Subsequently, they proceed to join forces with the Raider Battalion in their advance towards the southeastern end of the island.

Advancing against sporadic resistance, the line encounters increased opposition in the area separating the wooded ridge from the cultivated saddle. Particularly fierce resistance occurs in a ravine parallel to the line of advance, posing a threat to approaching forces. Opting to establish positions outside the ravine as darkness falls, Edson and his troops brace for the night.

Throughout the night, the Japanese launch a series of five attacks against the Marines lines, commencing at 22:30. These assaults comprise frontal charges as well as individual and small group infiltration attempts directed towards Edson’s command post, leading to instances of hand-to-hand combat with the Marines. Although the Japanese temporarily breach the Marine lines and manage to capture a machine gun, they are swiftly repelled. Despite sustaining additional casualties, the Marine lines hold firm for the remainder of the night. The Japanese incur significant losses during these attacks. Notably, Marine Edward H. Ahrens single-handedly neutralised 13 Japanese attackers before ultimately succumbing.

Gavutu and Tanambogo

At 12:00, Gavutu is assaulted by the U.S. Marine 1^st Parachute Battalion consisting of 397 men. The assault is scheduled for noon because there are not enough aircraft to provide air cover for the Guadalcanal, Tulagi, and Gavutu landings at the same time. The preceding naval bombardment damages the seaplane ramp, forcing the naval landing craft to land the Marines in a more exposed location on a nearby small beach. Almost immediately, Japanese machine gun fire begins inflicting heavy casualties, killing or wounding one in ten of the landing Marines as they scramble inland in an attempt to get out of the crossfire coming from the two islets.

Surviving Marines are able to deploy two M 1919 Browning machine guns to provide suppressive fire on Gavutu’s caves, allowing more Marines to push inland from the landing area. Seeking cover, the Marines become scattered and are quickly pinned down. Captain George Stallings, the battalion operations officer, directs Marines to begin suppressive fire with machine guns and mortars on the Japanese machine gun emplacements on Tanambogo. Shortly thereafter, American dive bombers drop several bombs on Tanambogo, diminishing some of the volume of fire from that location.

After about two hours, Marines reach and climb Hill 148. Working from the top, the Marines begin clearing the Japanese fighting positions on the hill, most of which still remain, with explosive charges, grenades, and hand-to-hand combat. From the top of the hill, the Marines are also able to put increased suppressive fire on Tanambogo. The Marine battalion commander on Gavutu radios General Rupertus with a request for reinforcements before attempting to assault Tanambogo.

Most of the 240 Japanese defenders on Tanambogo are aircrew and maintenance personnel from the Yokohama Air Group. Many of these are aircraft maintenance personnel and construction units not equipped for combat. However, despite their lack of proper weaponry, the Japanese engage the Americans in battle.

Meanwhile, General Rupertus detaches one company of Marines from the 1^st Battalion, 2^nd Marine Regiment on Florida Island to assist in assaulting Tanambogo, in spite of advice from his staff that one company is not enough. Incorrectly believing Tanambogo to be only lightly defended, this company attempts an amphibious assault directly on Tanambogo shortly after dark. Illuminated by fires started during a U.S. naval bombardment of the islet, the five landing craft carrying the Marines are hit by heavy fire as they approach the shore, with many of the U.S. Navy boat crews being killed or wounded, as well as heavily damaging three of the boats. Realising the position is untenable, the Marine company commander orders the remaining boats to depart with the wounded Marines, and he and 12 men who had already landed sprint across the causeway to cover on Gavutu. The Japanese on Tanambogo suffer 10 killed in the day’s fighting.

August 8th, 1942

Tulagi

During the early morning, six Japanese infiltrators concealed under the porch of the former British colonial headquarters ambush and fatally shoot three Marines. Within a span of five minutes, other Marines swiftly retaliate, eliminating the six Japanese with grenades.

Later that morning, following the arrival of reinforcements from the 2^nd Battalion, 2^nd Marines (2/2), the Marines encircled Hill 281 and the ravine. They subject both locations to sustained mortar bombardment by both raider and marine units throughout the morning before launching assaults starting around 15:00. Improvised explosive charges are utilised to neutralise Japanese defenders entrenched in numerous caves and defensive positions across the hill and ravine. These makeshift explosives effectively demolish individual Japanese fighting positions.

By the afternoon, significant Japanese resistance subsides. By nightfall, Tulagi is secured although a few remaining stragglers are discovered and eliminated over the subsequent days.

Gavutu and Tanambogo

Throughout the night, as the Japanese launch isolated attacks on the Marines stationed on Gavutu amid heavy thunderstorms, Vandegrift prepares to dispatch reinforcements to support the assault on Tanambogo. The 3^rd Battalion, 2^nd Marines (3/2), still aboard ships off Guadalcanal, receives orders to prepare for an assault on Tanambogo on August 8^th, 1942.

At 10:00, the 3/2 begins landing on Gavutu and aids in eliminating the remaining Japanese defences on the islet by midday. Following this, they ready themselves to attack Tanambogo. Meanwhile, the Marines on Gavutu provide covering fire. Despite requesting support from carrier-based dive bombers and naval gunfire bombardment, further assistance from carrier aircraft is called off after bombs are accidentally dropped on the Marines on Gavutu, resulting in the death of four Marines. However, the cruiser San Juan manages to shell Tanambogo for half an hour. The Marine assault on Tanambogo commences at 16:15, both by landing craft and from across the causeway. With the aid of two Marine Stuart light tanks, they begin to make progress against the Japanese defences.

During the assault, one of the tanks becomes stuck on a stump, leaving it vulnerable as it is surrounded by about 50 Japanese airmen. The Japanese set fire to the tank, resulting in the deaths of two crew members, while the others are severely beaten before being killed by Marine rifle fire. Around the burnt-out tank, the Marines discover 42 Japanese bodies, including those of the Yokohama executive officer and several seaplane pilots. Captain Miyazaki-san, the overall commander of the Japanese troops on Tanambogo, detonates explosives inside his dugout late in the afternoon.

Throughout the day, the Marines systematically destroy the caves on Tanambogo using dynamite, with most of them obliterated by 21:00.

Despite some sporadic attacks by surviving Japanese soldiers during the night, by noon on August 9^th, 1942, all resistance on Tanambogo ceases.

Aftermath

In the intense battle for Tulagi, a total of 307 Japanese soldiers and 45 U.S. troops lost their lives. Additionally, three Japanese soldiers are captured as prisoners of war.

The battle for Gavutu and Tanambogo results in the deaths of 476 Japanese defenders and 70 U.S. Marines and naval personnel. Out of the 20 Japanese prisoners captured during the battle, the majority are Korean labourers from the Japanese construction unit rather than combatants.

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