The Americans had discovered that the Japanese were building an airfield on Guadalcanal, and that became the primary target for Operation Watchtower. The 1st Marine Division, with the 1st Raider Battalion attached, received the assignment to invade Guadalcanal and Tulagi as well.
The 1st Raiders received definitive word on Watchtower on 20 July. They would seize Tulagi, with the 2d Battalion, 5th Marines, in support. The 1st Parachute Battalion would take the conjoined islets of Gavutu-Tanambogo. The 1st Marine Division, less one regiment in reserve, would capture the incomplete airfield on Guadalcanal.
Edson offered to make amphibious reconnaissance patrols of the objectives, but the naval commander rejected that idea. Most of the information on Tulagi would come from three Australians, all former colonial officials familiar with the area. Tulagi was 4,000 yards long and no more than 1,000 yards wide, and a high ridge ran along its length, except for a low, open saddle near the southeast end. The only suitable landing beaches from a hydrographic standpoint were those on either side of this low ground, since coral formations fringed the rest of the island. Intelligence officers estimated that the island held several hundred men of the Japanese Special Naval Landing Force; these were elite troops of proven fighting ability. Aerial reconnaissance indicated they were dug in to defend the obvious landing sites. Planners thus chose to make the assault halfway up the western coast at a place designated as Beach Blue. They wisely decided to make the first American amphibious assault of the war against natural obstacles, not enemy gunfire.
On the morning of 7 August the task force hove to and commenced unloading in what would become known as Iron-bottom Sound. Although Edson’s men had trained hard on their rubber boats, they would make this landing from Higgins boats. After a preliminary bombardment by a cruiser and destroyer, the first wave, composed of Companies B and D, headed for shore. Coral forced them to debark and wade the last 100 yards, but there was no enemy opposition. Companies A and C quickly followed them. The four rifle companies spread out across the waist of the island and then advanced in line to the southeast. They met only occasional sniper fire until they reached Phase Line A at the end of the ridge, where they halted as planned while naval guns fired an additional preparation on the enemy defenses.
The attack jumped off again just before noon, and promptly ran into heavy Japanese resistance. For the remainder of the day the raiders fought to gain control of the saddle from the entrenched enemy, who would not surrender under any circumstances. The Marines quickly discovered that their only recourse was to employ explosives to destroy the men occupying the caves and bunkers. As evening approached, the battalion settled into defensive lines that circled the small ridge (Hill 281) on the tip of the island. The 2d Battalion, 5th Marines, had already scoured the remainder of the island and now took up positions in the rear of the raiders.
The Japanese launched their classic banzai counterattack at 2200 that night. The initial effort punched a small hole in the raider lines between Companies A and C. A second assault, which might have exploited this gap, instead struck full against Company As front. This time the raiders held their ground. For the remainder of the night the Japanese relied on infiltration tactics, with individuals and small groups trying to make their way into the American rear by stealth. By this means they attacked both the 2d Battalion’s command post (CP) and the aid station set up near Blue Beach. They also came within 50 yards of the raider CP. Edson tried to call for reinforcements, but communications were out.
In the morning things looked much better, just as they had on Makin. At 0900 two companies of the 5th Marines passed through raider lines and swept over the southern portions of Hill 281. The remaining enemy were now isolated in a ravine in the midst of the small ridge. After a lengthy barrage by the 60mm mortars of Company E and their heavier 81mm cousins of the rifle battalion, infantrymen from both outfits moved through the final enemy pocket. Grenades and dynamite were the weapons of choice against the Japanese still holed up in their caves and dugouts. At 1500 Edson declared the island secured.
That did not mean the fighting was entirely over. For the next few days Marines scoured the island by day, and fended off occasional infiltrators at night, until they had killed off the last enemy soldier. In the entire battle, the Raiders suffered losses of 38 dead and 55 wounded. There were an additional 33 casualties among other Marine units on the island. All but three of the 350 Japanese defenders had died.