In general, size is what distinguishes the two, boats being smaller than ships, but the words’ usage is more complicated than any one simple rule of absolute size can describe. The US Navy generally follows the “boats are smaller” rule, referring to its smaller vessels as boats and its larger ones as ships.
What are military boats called?
A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces of a state. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuverable than merchant ships.
- Aircraft carriers.
- Amphibious assault ships.