VMS Help FORTRAN, Statements, EXTERNAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Specifies that a name is a global symbol defined outside the
  program unit.  Statement format:

     EXTERNAL v[,v]...
     EXTERNAL *v[,*v]...

     v  Is the symbolic name of a user-supplied subprogram, or
        the name of a dummy argument associated with the name
        of a subprogram.  If you name an intrinsic subprogram,
        that name becomes disassociated from the intrinsic
        subprogram and is assumed to be the name of an external
        element.  (The INTRINSIC statement allows intrinsic
        function names to be used as arguments.)

     *  Is permitted only with the -nof77 option.

  You must use EXTERNAL statements in the following cases:

   -  To identify subprogram or entry point names passed as actual
      arguments

   -  To identify a block data program unit that will reside in a
      library module not explicitly referenced at link time.

  You do not need to use an EXTERNAL statement to identify a
  subprogram or entry point name used as the object of a CALL
  statement or function reference; these names are recognized as
  external implicitly.