The portable steel pillbox Steel machine gun pillboxes (Kiju tochika) were only encountered during the November 1943 assault on Betio Island. Tarawa Atoll, but may originate from the time of the Russo-japanese War. The pillboxes were probably installed just prior to the assault. The defense was controlled from a number of these pillboxes emplaced at approximately 300-yard intervals around the island's perimeter behind the 3-5ft-high seawall. Serving as company command posts, their 8ft height was important given the island's 6ft elevation. As the Marines possessed few bazookas and flamethrowers, it required a near direct naval gun or Sherman hit to destroy them, The hexagonal pillboxes were prefabricated, and erection required a derrick or A-frame. The side panels sloped 15 degrees: five of them were assembled from three riveted, trapezoid plates. The double walls were 0.25in. thick with a sand filled 12in gap between them. Most were banked with sand on the outside, but this seldom reached to the upper edge of the bottom plates. Two examples were capped with I2in of concrete. The interior had a steel celling, level with the upper edge of the middle side plates. A 2.5ft long hexagonal shaft ran through the ceiling to a roof hatch. The top portion around the shaft was filled with sand. The shaft was fixed with a metal seat, a voice tube to the lower compartment, and a 32in diameter roof hatch from which to observe. There were no observation slits or periscope, forcing the observer to expose his head. The hatch consisted of six 0.5in thick triangular segments, each of which could be opened separately and swung outward. The lower compartment housed two HMG's for which integral mounts were provided. The Japanese numbered the side panels clockwise. A 2 ft x 5ft, 0.5in thick steel, two-piece sliding door was set in the No. I panel (rear). This side was not double-walled, except for the top plate around the hatch access shaft. The other panels were Nos. 2 and 6 (solid, not shown), Nos. 3 and 5 (machine gun ports), and No. 4 (3 x 5in. vision slot). The firing ports measured 18 x 24in internally and had sliding, two-piece, 0.5in thick steel shutters, the ports outer wall openings were 36in on the sides and top, and 42in on the bottom.