At the outbreak of World War I Bryan was still at school and was too young to enlist. In 1915, aged 17, he joined the Territorial Force, being awarded a commission as a 2nd Lieutenant in the 5th Battalion, the Manchester Regiment, the same battalion his brother Jack was serving in and the brother's father had been a Lieutenant-colonel in.
When World War I broke out, Bryan was still a student and not old enough to enlist. However, he joined the Territorial Force in 1915 at just 17 years old and was commissioned as a 2nd Lieutenant in the 5th Battalion of the Manchester Regiment, where his brother Jack was fighting alongside him, and whose father had previously commanded a battalion.