The model depicts a bunker or gun pit still under construction. The bunker is built from palm log walls with a coral infill and 2 recesses for ammunition.
The advantage of the ammunition recesses are that they allow artillery or machine guns mounted on square bases to sit closer to the embrasure.
The photos show a Japanese anti tank gun mounted on a 50mm x 60mm base inside the bunker.
Width 98mm, Height 25mm, Depth 105mm (All dimensions are approximate)