Acting Pilot Officer is the lowest commissioned grade in the Royal Air Force

Royal Air Force

The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

, being immediately junior to Pilot Officer

Pilot Officer

Pilot officer 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...

. Unlike other RAF ranks which officers may hold in an acting capacity, Acting Pilot Officer is maintained as a separate grade. It normally denotes an officer who has recently been commissioned and joined as a non-graduate direct entrant. Acting Pilot Officer is not an actual rank, and APOs are later regraded to Pilot Officer, not promoted.
Although Acting Pilot Officer has a NATO ranking code of OF-1, neither the British Army

British Army

The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

, Royal Marines

Royal Marines

The Corps of Her Majesty's Royal Marines, commonly just referred to as the Royal Marines , are the marine corps and amphibious infantry of the United Kingdom and, along with the Royal Navy and Royal Fleet Auxiliary, form the Naval Service...

 nor Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 has an exactly equivalent rank. As Acting Pilot Officers are junior to Second Lieutenant

Second Lieutenant

Second lieutenant is a junior commissioned officer military rank in many armed forces.- United Kingdom and Commonwealth :The rank second lieutenant was introduced throughout the British Army in 1871 to replace the rank of ensign , although it had long been used in the Royal Artillery, Royal...

s in the British Army or the Royal Marines and to Royal Navy Sub-Lieutenant

Sub-Lieutenant

Sub-lieutenant is a military rank. It is normally a junior officer rank.In many navies, a sub-lieutenant is a naval commissioned or subordinate officer, ranking below a lieutenant. In the Royal Navy the rank of sub-lieutenant is equivalent to the rank of lieutenant in the British Army and of...

s, the rank is the most junior commissioned rank in the British Armed Forces.

Senior cadets on a University Air Squadron

University Air Squadron

University Air Squadrons are training units of the Royal Air Force which primarily provide basic flying training, force development and adventurous training to undergraduate students at British universities...

may become Acting Pilot Officers.

The rank insignia is identical to that of a Pilot Officer, consisting of a thin blue band on slightly wider black band. This is worn on both the lower sleeves of the tunic or on the shoulders of the flying suit or the casual uniform.