A collective noun refers to a group of people or things. When "ships" refers to a group of vessels, it acts as a collective noun.
Here are some examples:
* "The fleet of ships sailed into the harbor." (fleet is a collective noun, but "ships" also acts as one, referring to the group of vessels)
* "The ships were all at anchor." (Here, "ships" refers to a group of vessels)
However, "ships" can also be a plural noun, referring to multiple individual vessels.
* "There were three ships in the bay." (Here, "ships" is a plural noun referring to individual vessels)
So, whether "ships" is a collective noun or a plural noun depends on the context.