Air commodore is a one-star rank and the most junior air officer rank, being immediately senior to group captain and immediately subordinate to air vice-marshal. It has a NATO ranking code of OF-6 and is equivalent to a commodore in the Royal Navy or a brigadier in the British Army or the Royal Marines. Unlike these two ranks, however, it has always been a substantive rank. Additionally, air commodores have always been considered to be air officers whilst Royal Navy commodores have not since the Napoleonic Wars been classified as officers of flag rank, and British Army brigadiers have not been considered to be general officers since 1922 when they ceased to be titled as brigadier-generals. In other NATO forces, such as the United States Armed Forces and the Canadian Armed Forces, the equivalent one-star rank is brigadier general.
In the present-day RAF, air commodores typically hold senior appointments within groups, acting directly in support of the air officer commanding. However, during the inter-war period, and in the case of the contemporary No. 83 Expeditionary Air Group, the air officer commanding held or holds air commodore rank. In the Air Training Corps, an appointed air commodore holds ultimate authority over the cadet organisation as the Commandant Air Cadets.
On 1 April 1918, the newly created RAF adopted its officer rank titles from the British Army, with officers at what is now air commodore holding the rank of brigadier-general. In response to the proposal that the RAF should use its own rank titles, it was suggested that the RAF might use the Royal Navy's officer ranks, with the word "air" inserted before the naval rank title. Although the Admiralty objected to this simple modification of their rank titles, it was agreed that the RAF might base many of its officer rank titles on Navy officer ranks with differing pre-modifying terms. It was also suggested that air-officer ranks could be based on the term "ardian", which was derived from a combination of the Gaelic words for "chief" (ard) and "bird" (eun), with the term "fourth ardian" or "flight ardian" being used for the equivalent to brigadier-general and commodore. However, the rank title based on the Navy rank was preferred and air commodore was adopted on 1 August 1919.
The rank insignia is a light-blue band on a broad black band worn on both the lower sleeves of the tunic or on the shoulders of the flying suit or the casual uniform. On the mess uniform, air commodores wear a broad gold ring on both lower sleeves.