 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 largest island, Betio.When the Americans landed, nearly 5,000 Imperial Japanese Navy Land 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.