Eight artillery casemates, forty infantry casemates or blockhouses and fifteen command posts were built. There are crumbling remnants of Japanese blockhouses and pillboxes around Roi-Namur. "Johnston" shelled an observation tower and several blockhouses, pillboxes, and dugouts along the beach. At the same time, an elaborate system of caves, concrete blockhouses, and pillboxes were established. He described a fortification with four blockhouses, manned by riflemen. A number of forts, blockhouses and timber buildings were handed over to the Americans. Along the canal there were tank traps, bunkers and blockhouses. Detachments occupied networks of blockhouses and provided complements for armoured trains. The airfield was protected by wire, minefields and blockhouses. Bunkers are mostly underground, in contrast to blockhouses which are mostly above ground. A gravel airstrip, artesian bores and concrete blockhouses remain. Guards stationed at the blockhouses regularly patrolled the area. Not one bridge where one of these blockhouses was sited and manned was blown. Around 441 were solid masonry blockhouses, many of which stand today. The bridges were defended by blockhouses equipped with machine-guns.