If you read older flying materials and books like the classic Stick and Rudder by Wolfgang Langewiesche, aircraft are very frequently and consistently referred to as "ships". Many movies and videos from World War 2 also use the word, based on what I've found on Youtube.
But today "ship" isn't used widely - if at all - and it now seems very old-fashioned. What happened? When and why did "ship" stop being a common term for an aircraft?
(Cross-posted from aviation.SE)