[DaveyJ576]

A ship is generally defined as any vessel that is capable of open ocean, long term, independent steaming without the support of a mothership. Examples: Battleship, Cruiser, Aircraft Carrier, Destroyer, Oiler, Ammo Ship, and yes Submarines.

A craft is generally the exact opposite, i.e. it will operate in the "brown water" regions in harbors, rivers, or close to shore. It will have an endurance usually measured in hours, maybe a day or two at the most, and it will require the direct support of a shore base or mothership to complete its mission.

A boat is any ship or craft that operates in fresh water, or one that is normally carried onboard another ship. It will usually meet the definition of a craft.

A submarine is officially considered by the USN to be a ship. In official documents and correspondence it is refered to as such. However, on a person to person basis, the term "ship" is rarely used to describe a submarine. How did subs come to be called boats?

Our earliest submarines were quite small and were designed for harbor defense only. They perfectly met the definition of "craft" that I outlined above. For long transfers from port to port, they were either towed or hauled out of the water and placed on the deck of a ship. Thus the term boat. By 1918, the technology had rapidly improved and the USN had submarines capable of blue water operations and they should have been rightly called ships. However, the term boat had become so ingrained into Navy lexicon that it stuck around, although in a somewhat un-official capacity. Even today, our massive Ohio class SSBN's armed with 24 Trident ballistic missiles are still called boats. It is exceedingly rare for you to hear our submariners to refer to their boats by any other term.