Porthole

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.

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).

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 aft castles.

The porthole is primarily a circular glass disk, known as a portlight, encased in a metal frame that is bolted securely into the side of a ship's hull.

Hinged porthole windows and storm covers are accessible from inside the ship's hull and are typically fastened to their closed positions by hand-tightening several pivoting, threaded devices, commonly referred to as "dogs".

Older portholes can be identified by the protruding collar of their base plate which may be up to several inches deep, thus accommodating the thickness of a wooden hull.

The porthole's thick glass and rugged construction, tightly spaced fasteners, and its round shape all contribute to its purpose of maintaining hull strength and withstanding the pressure of storm waves crashing against it.