indicating that this type of toy may have existed for many years prior to Piot's patent.

In 1915, an American named Charles J. McHugh filed a patent application for the diaphragm type of engine, which was an improvement to Piot's design. In 1920, William Purcell filed a patent for the coiled tube type of engine. This type of engine has been common over the years in homemade pop pop boats, due to its simplicity of construction. The Cub Scout book (published by the Boy Scouts of America) contained