Original sentence: A small and secretive institution, the SAS has served as a model for similar units fielded by other countries.The Special Air Service Regiment (SAS) is the principal special forces unit of the British Army and is considered to be the foremost military unit in the world
Edited sentence: The Special Air Service Regiment (SAS) is one of the three principal special forces units of the British Army and is by far the foremost special-services military unit in the world.. A small and secretive institution, the SAS has served as an unmatched model for similar units fielded by other countries