In 1915, during the First World War, he was appointed Chief of Staff for the Mediterranean Expedition, commanded by Ian Hamilton. He was regarded by many of the Australians involved in that effort as "arrogant and incompetent". After the failure of the Mediterranean expedition, Braithwaite was recalled to London. He was later assigned to command of the 62nd (2nd West Riding) Division, a Territorial Force (TF) formation, which was posted to France in January 1917. Here he experienced considerable success. Although the division struggled to make headway during the Battle of Arras, it proved a solid and reliable unit during the German Spring Offensive the following year. Following success in repelling German advances at Bullecourt and Cambrai, he was given command of IX Corps on 13 September 1918 and later XII Corps.