Complex sentence: With the assistance of other historians and the Western Australian Museum, Mearns researched the battle by focusing on primary source documents, during which he discovered several archive files and "Kormoran" diaries previously believed to be lost.
Split into simpler sentences: With the assistance of other historians and the Western Australian Museum, Mearns researched the battle, focusing on primary source documents. He discovered several archive files and "Kormoran" diaries previously believed to be lost.