Tarawa was primarily defended by two SNLF (Special Naval Landing Force) units each about the size of a large battalion. These were tailor-made for the island's defense. Both consisted primarily of gun crews manning heavy weapons. In each there was also about a reinforced company of infantry for general defense. All of these troops were IJN sailors seconded to function as combat troops (the Japanese had nothing equivalent to the US Marine Corps). There was also a construction battalion with a mix of low grade Japanese soldiers and Korean slave labor amounting to about 900 men.
The Koreans pretty much refused to fight except under threat and the Japanese soldiers in this unit were armed with just small arms.

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