VMS Help DELETE, file, Qualifiers, /BITMAP  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BITMAP=n,x

    Enables the system manager to delete one or more active bitmaps
    to make memory resources available. If a bitmap is deleted, then
    former virtual unit members can only be added with a full copy.

    Requires ownership of the device or VOLPRO protection.

    For additional information on bitmaps, refer to Volume Shadowing
    for OpenVMS.