katajaluoto island is a narrow, north-south oriented island located approximately half way on the line between rysäkari and harmaja. a 10-inch battery built on the widest part divides the island into northern and southern parts. the construction of the battery began in october 1914 and the guns were placed on their foundations in early 1915 with the parapet and traversal walls completed in autumn 1915. katajaluoto battery is the narrowest of the 10-inch batteries. the northern shore of the island has a heavily fortified concrete bunker used as mine control bunker, telephone exchange and electrical station. the island had a 150 cm searchlight. there is also a unique fortified concrete latrine on the eastern shore.