The Special Investigation Branch (SIB) is the name given to the detective branches of all three British military police arms: the Royal Navy Police, Royal Military Police and Royal Air Force Police. It is most closely associated with the Royal Military Police, which has the largest SIB. SIB members usually operate in plain clothes, although they may wear uniform when serving overseas. Members are usually senior non-commissioned officers (sergeants or petty officers or above) or commissioned officers, although the Royal Air Force SIB also employs corporals.