In the Royal Flying Corps, officers were designated pilot officers at the end of pilot training. As they retained their commissions in their customary ranks (usually second lieutenant or lieutenant), and many of them had been seconded from their ground units, the designation of pilot officer was a position title rather than a rank.
On 1 April 1918, the newly created RAF adopted its officer rank titles from the British Army, with Royal Flying Corps second lieutenants becoming second lieutenants in the RAF. Consideration was given to renaming second lieutenants as ensigns. However, when the RAF's own rank structure was introduced on 1 August 1919, RAF second lieutenants who were qualified pilots were redesignated pilot officers, a rank which has been in continuous use ever since. Those who were not qualified pilots were redesignated observer officers, but this was later phased out and all officers of this rank became pilot officers.