Porthole

A porthole, sometimes called bull's-eye window or bull's-eye, is a generally circular window used on the hull of ships to admit light and air. Though the term is of maritime origin, it is also used to describe round windows on armored vehicles, aircraft, automobiles (the Ford Thunderbird a notable example) and even spacecraft.

On a ship, the function of a porthole, when open, is to permit light and fresh air to enter the dark and often damp below-deck quarters of the vessel. It also affords below-deck occupants a limited, but often much needed view to the outside world. When closed, the porthole provides a strong water-tight, weather-tight and sometimes light-tight barrier.

A porthole on a ship may also be called a sidescuttle or side scuttle (side hole), as officially termed in the International Convention for the Safety of Life at Sea. This term is used in the U.S. Code of Federal Regulations. It is also used in related rules and regulations for the construction of ships. The use of the word "sidescuttle" instead of "porthole" is meant to be broad, including any covered or uncovered hole in the side of the vessel.

According to the Navy Department Library, the word "porthole" has nothing to do with its location on the port side of a ship, but originated during the reign of Henry VII of England (1485). The king insisted on mounting guns too large for his ships and therefore the conventional methods of securing the weapons on the forecastle and aftcastle could not be used. A French shipbuilder named James Baker was commissioned to solve the problem, which he did by piercing the ship's sides so the cannon could be mounted inside the fore and after castles. For heavy weather and when the cannons were not in use, the openings were fitted with covers, that were called porte in French, meaning "door". "Porte" was Anglicized to "port" and later corrupted to porthole. Eventually, it came to mean any opening in a ship's side whether for cannon or not.

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