after the attack on Pearl Harbor, in order to protect their south-eastern flank from allied counterattacks, and isolate Australia. The islands were to become a staging post for the planned invasion of the Ellice Islands by the Japanese, under the codename Operation FS, but their setback at the Battle of the Coral Sea delayed the plans, and their defeat at the Battle of Midway and later in the Solomon Islands put a definitive end to it. Following Carlson's Raiders' diversionary Raid on Makin Island and the defeat at Guadalcanal, the Japanese command was growing aware of the vulnerability and strategic significance of the Gilbert Islands, and started adopting a defensive stance. Although Imperial leaders wanted to heavily fortify the Marianas and Palau before the Americans could get there, commanders in the outer islands were told to try and hold the island as long as possible. Fortifications were quickly improved by the Japanese, starting in March 1943. Makin Atoll had a seaplane base built on the main island of Butaritari, while Tarawa housed barely enough room for an airfield on its main harbour island, Betio. Battle of Tarawa When the Americans landed, in the Battle of Tarawa fought on 20–23 November 1943, nearly 5,000 Imperial Japanese Naval Landing Forces, among them 3,000 Special Naval Landing Forces and 1,247 construction laborers were stationed on Tarawa; the Makin Islands, in contrast, were only held by a total of 798 combat troops, including some 100 isolated Japanese aviation personnel. A detachment of soldiers from Tarawa island also occupied the island of Abemama in September 1942, and though initially numbering about 300, by the time the Americans invaded the island in November 1943, most of them had been evacuated back to Tarawa, leaving only 25 Special Naval Landing Forces behind to defend the island. Lieutenant Junior Grade Seizo Ishikawa, the Japanese commander in charge of defending Makin, ordered his troops to build extensive fortifications on the island. These included coastal defense guns, anti-tank gun positions, machine gun emplacements, rifle pits, deep tank barriers with anti-tank guns and barbed wire. These were designed to hold the island until reinforcements could arrive. On Tarawa, Keiji Shibazaki had 4,836 troops, including around 2,600 Special Naval Landing Forces, 1,000 Japanese construction workers and 1,200 Korean laborers. He planned to use these units to primarily defend Betio, the largest island in the atoll. Betio was the site of a crucial