Complex sentence: In 1902 the RML guns were replaced by 2 9.2 "and 2 6" BL guns, and before the First World War the walls were further strengthened with substantial earthwork embankments.
Split into simpler sentences: In 1902 the RML guns were replaced by 2 9.2 "and 2 6" BL guns. Before the World War 1, the walls were further strengthened with substantial earthwork embankments.