Complex sentence: The Operations Staff, George Harper tried to convince MacDonogh to give French only the kind of information that suited his preconceived ideas and failed, Intelligence played a critical part during the Battle for Ypres.
Split into simpler sentences: The Operations Staff, George Harper tried to convince MacDonogh to give French only the kind of information that suited his preconceived ideas, and failed. Ultimately, intelligence played a critical part during the Battle for Ypres.