Opera hat described as: Some sources have taken this to describe an early folding top hat, although it is not explicitly stated whether Dollman's design was specifically for male or female headgear. Dollman's patent expired in 1825. Operating from Poissy, Paris, France, around 1840, Antoine Gibus's design for a spring-loaded collapsible top-hat proved so popular that hats made to it became known as "gibus". They were also often called "opera hats" due to the common practice of storing them in their flattened state under one's seat at the opera, though the term can also refer to any tall formal men's hat. The
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