I believe you must edit your httpd.conf file and make sure the DirectoryIndex section has the file names you want to be served as the default index files for a directory
normally the default is index.html so if you don't have that file in your directory
http://theftp.dhs.org/index.html you have to add another name to the httpd.conf file or
you may get a page not found error or a directory listing if you have Public read permissions for that directory