This combination knife and form was left at the Battle of Germantown, in Pennsylvania, by a member of the Hessian Army. Made of wood and steel, it measures about 10.6″ open, and 5.1″ closed. For source and more details, click here.
Image from: http://www.cr.nps.gov/museum/exhibits/revwar/image_gal/morrimg/comboforknife.html