Opera hat which means hat, and "claque", which means "tap" or "click". The "chapeau claque" is thus a hat that folds with a click, and unfolds likewise. In English the hat model is usually referred to as a "collapsible top-hat", "gibus" or more often "opera hat"- The construction may originally have been inspired by an historical hat model called "chapeau bras" ("arm hat"), made as bicorne or tricorne to be carried folded under the arm On May 5, 1812, a London hatter called Thomas Francis Dollman patented a design for "an elastic round hat" supported by ribs and springs. His patent was
Operation Top Hat Operation Top Hat Operation Top Hat was a "local field exercise" conducted by the United States Army Chemical Corps in 1953. The exercise involved the use of Chemical Corps personnel to test biological and chemical warfare decontamination methods. These personnel were deliberately exposed to these contaminants, so as to test decontamination. In June 1953 the United States Army formally adopted guidelines regarding the use of human subjects in chemical, biological, or radiological testing and research. The guidelines were adopted per an Army Chief of Staff memo (MM 385) and closely mirrored the Nuremberg Code. These guidelines also required that all