Regimental Sergeant Major (rank)

A Regimental Sergeant Major, usually abbreviated to RSM, is an appointment held by warrant officers class 1 (WO1) in the British Army, the Royal Marines and in the armies of many Commonwealth and former Commonwealth nations, including Ireland, Australia and New Zealand; and by chief warrant officers (CWO) in the Canadian Forces. Only one WO1/CWO holds the appointment of RSM in a regiment or battalion, making him the senior warrant officer; in a unit with more than one WO1, the RSM is considered to be "first amongst equals". The RSM is primarily responsible for maintaining standards and discipline and acts as a parental figure to his or her subordinates and also to junior officers, even though they technically outrank the RSM.

In the British Army, the RSM is addressed as "Sir" or "Ma'am" by his or her subordinates. In the Household Cavalry, the appointment is Regimental Corporal Major (RCM).

In the Royal Marines, Regimental Sergeant Major was an actual rank (and equivalent to Warrant Officer class I in the Army) until the Royal Marines themselves re-adopted the ranks of warrant officer classes I and II in 1973 (although the term continued to be used interchangeably for Warrant Officers Class I until at least 1981). The most senior warrant officer in the Royal Marines holds the appointment of Corps Regimental Sergeant Major.