Top hat top hat is a hard, black silk hat, with fur now often used. The acceptable colors of hats are much as they have traditionally been, with "white" hats (which are actually grey), a daytime racing color, worn at the less formal occasions demanding a top hat, such as Royal Ascot, or with a morning suit. In the U.S. top hats are worn widely in coaching, a driven horse discipline as well as for formal riding to hounds. The collapsible silk opera hat, or "crush hat", is still worn on occasions, and black in color if worn with evening wear as
Operation Top Hat informed of the tests. 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