Library /sys$common/syshlp/latcp$help.hlb SPAWN, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 DCL-command

    Specifies a DCL command. If you specify a DCL command, LATCP
    executes the command in a subprocess. Control returns to LATCP
    when the DCL command terminates.

    If you do not specify a DCL command, LATCP creates a subprocess
    and you can then enter DCL commands. You can continue your LATCP
    session by logging out of the spawned subprocess or by attaching
    to the parent process with the DCL ATTACH command.