shore duty vs duty assignment

shore duty and duty assignment both are nouns.

Word	Noun	Adjective	Verb	Adverb
shore duty	Yes	No	No	No
duty assignment	Yes	No	No	No

As nouns, duty assignment is a hypernym of shore duty; that is, duty assignment is a word with a broader meaning than shore duty:

shore duty: naval service at land bases
duty assignment: a duty that you are assigned to perform (especially in the armed forces)

Other hypernyms of shore duty include assignment.

shore duty (noun)	duty assignment (noun)
naval service at land bases	a duty that you are assigned to perform (especially in the armed forces)