Horseshoe to the modern hoof boot. Historians differ on the origin of the horseshoe. Because iron was a valuable commodity, and any worn out items were generally reforged and reused, it is difficult to locate clear archaeological evidence. Although some credit the Druids, there is no hard evidence to support this claim. In 1897 four bronze horseshoes with what are apparently nail holes were found in an Etruscan tomb dated around 400 B.C. The assertion by some historians that the Romans invented the "mule shoes" sometime after 100 BC is supported by a reference by Catullus who died in 54 BC.
Casing (submarine) Casing (submarine) The casing of a submarine is a light metal structure, usually incorporating a deck, built over the upper surface of the vessel's pressure hull. The pressure hull of a submarine is usually cylindrical and possesses a low freeboard when in the water, which makes walking on the hull when on the surface dangerous in high seas or rough weather. The casing provides a flat and therefore safer platform for personnel to walk on. The casing is outside the pressure hull and free-flooding so is usually perforated with numerous holes, allowing water to enter and trapped air to escape