navy vs armed service

navy and armed service both are nouns.

Word	Noun	Adjective	Verb	Adverb
navy	Yes	No	No	No
armed service	Yes	No	No	No

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

navy: an organization of military vessels belonging to a country and available for sea warfare
armed service: a force that is a branch of the armed forces

Other hypernyms of navy include military service, service.

navy (noun)	armed service (noun)
a dark shade of blue	a force that is a branch of the armed forces
an organization of military vessels belonging to a country and available for sea warfare