Azimuteros are commando units trained in the use of the compass (hence the name) and in night fighting.  There is very little known about the Azimuteros as they appear to have been a rare unit, if they existed at all.  It seems they were used to lead night attacks, to guide the rest of the forces and to act as shock troops.*
*
If allowed, only one of these formations should normally be purchased for any campaign or free-standing scenario.