The term "port hole" originated during the reign of Henry VI of England (1485). King Henry insisted on mounting guns too large for his ship, and the traditional methods of securing these weapons on the forecastle and aftcastle could not be used.
A French shipbuilder named James Baker was commissioned to solve the problem. He put small doors in the side of the ship and mounted the cannon inside the ship. These doors protected the cannon from weather and were opened when the cannon were to be used. The French word for "door" is "porte" which was later Anglicized to "port" and later went on to mean any opening in the ship's side, whether for cannon or not.