From the awards manual... a lot left up to discretion.. Bottom line (for me), anything noteworthy done operationally. Cleaning up a beach while stashed? no.
NAM Eligibility Requirements. Awarded to members of
the Armed Forces of the grade of lieutenant commander or major
and junior thereto, for service performed on or after 1 May
1961. The award may be authorized for meritorious service or
achievement in a combat or non-combat situation, based on
sustained performance or specific achievement of a superlative
nature, and shall be of such merit as to warrant more tangible
recognition than is possible by a fitness report or performance
evaluation, but which does not warrant a Navy and Marine Corps
Commendation Medal.
(1) Professional achievement that merits the award
must:
(a) Clearly exceed that which lS normally
required or expected, considering the individual's grade or
rate, training, and experience; and,
Be an important contribution of benefit to
the United States and the Naval Service.
(2) Leadership achievement that merits the award
must:
(a) Be noteworthy;
(b) Be sustained so as to demonstrate a high
state of development or, if for a specific achievement, be of
such merit as to earn singular recognition for the act(s); and,
(c) Reflect most creditably on the efforts of
the individual toward the accomplishment of the unit mission.