Merrimac vs USS Merrimack

Merrimac and USS Merrimack both are nouns.

Word	Noun	Adjective	Verb	Adverb
Merrimac	Yes	No	No	No
USS Merrimack	Yes	No	No	No

As nouns, Merrimac and USS Merrimack are synonyms defined as:

Merrimac and USS Merrimack: an ironclad vessel built by the Confederate forces in the hope of breaking the blockade imposed by the North

Merrimac (noun)	USS Merrimack (noun)
an ironclad vessel built by the Confederate forces in the hope of breaking the blockade imposed by the North	an ironclad vessel built by the Confederate forces in the hope of breaking the blockade imposed by the North