in the back end of the site go to "Extensions > Template Manager" check the checkbox next to the Gantry template then select the "Duplicate" button (upper right).
Now open the new copy of the Gantry template and go tot he menu tab check the Menu Control checkbox and toggle it to the "Off" position. Then go to the "Assignments" tab and check the "Home" menu item check box. You can name this copy of the Gantry template to "rt_gantry_j16 - HOME" and save.