navy man vs serviceman

navy man and serviceman both are nouns.

Word	Noun	Adjective	Verb	Adverb
navy man	Yes	No	No	No
serviceman	Yes	No	No	No

As nouns, serviceman is a hypernym of navy man; that is, serviceman is a word with a broader meaning than navy man:

navy man: a serviceman in the navy
serviceman: someone who serves in the armed forces; a member of a military force

Other hypernyms of navy man include man, military man, military personnel.

navy man (noun)	serviceman (noun)
a serviceman in the navy	someone who serves in the armed forces; a member of a military force