Pilot officer (Plt Off officially in the RAF; PLTOFF in the RAAF and RNZAF; formerly P/O in all services, and still often used in the RAF) is the lowest commissioned rank in the Royal Air Force and the air forces of many other Commonwealth countries. It ranks immediately below flying officer. It normally denotes an officer who has elected to join as a non-graduate direct entrant officer, as those with degrees usually serve only a week at the rank after graduation from the RAF College Cranwell. Some newly commissioned officers hold the lower grade of acting pilot officer.
It has a NATO ranking code of OF-1 and is equivalent to a second lieutenant in the British Army or the Royal Marines. The Royal Navy has no exactly equivalent rank, and a pilot officer is senior to a Royal Navy midshipman and junior to a Royal Navy sub-lieutenant. In the Australian Armed Forces, the rank of pilot officer is equivalent to acting sub lieutenant in the Royal Australian Navy.
The equivalent rank in the Women's Auxiliary Air Force (WAAF) was "assistant section officer".
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.