On the outbreak of war Colonel Harper was placed in charge of the Oa (planning operations and written orders) section at BEF GHQ. The I (intelligence) and Ob (written records) sections were subordinate to Oa, making Oa in practice something of a bottleneck. He had a poor relationship with the BEF Chief of Staff Murray, as he was used to working with Murray's deputy and rival Wilson. On 24 August (the day after the Battle of Mons) Harper refused to do anything for Murray, so that Lord Loch had to write messages even though it was not his job. Wilson had to intercede to prevent French from sacking Harper (Wilson diary 7 Sep) but a week later recorded (Wilson diary 14 Sep), that Murray and Harper argued constantly.