If you need stronger defences than just earthworks deweycat has released an stl for the two story Japanese Command Bunker on Tarawa. This was a two-storey concrete building with a roof top gun position, situated near the airfield on the island. The bunker took a battering from the extensive naval and air bombardment, but ironically the Japanese commander Shibazaki was killed when he stepped out to confer with other officers, as the bombardment had broken all communication cables to the command bunker.
This bunker .stl has been sized to fit on most FDM printer beds as a four-part print; ground floor, middle floor and roof, with an exterior stairway up the back. None of the parts should be glued as they have been designed to fit with bayonet style lugs to allow the floors to be separated for floor by floor fighting. The stl set comes with a clean pre-barrage version of the bunker as well as a battle-damaged model.