 Complete the following phrase:  After the outbreak of the First World War, Davidson joined the III Corps as a staff officer and participated in the First Battle of the Marne, First Battle of the Aisne and the First Battle of Ypres. After the formation of the First Army in 1915 he became the operations officer for Douglas Haig, the Army commander. As operations officer Davidson was the principal organiser of the Battle of Neuve Chapelle, Battle of Loos and the 