While improper relationships within the same chain of command are the most obvious, there is no blanket requirement under the UCMJ that the relationship be within the same chain of command to be improper.
"Custom" is a long-established practice which, by common consent, has attained the force of law within the military.
The relevant custom within the Marine Corps is that "duty, social, and business contacts among Marines of different grades will be consistent with traditional standards of good order and discipline and the mutual respect that has always existed between Marines of senior grade and those of lesser grade."
Improper personal relationships between Marines occupying different positions may influence the senior's judgment as to mission accomplishment.
The threat to discipline and order need not be perceived by the parties involved in the fraternization. It is enough that the ill effects could be perceived by a reasonably prudent Marine experienced in military leadership. Thus, each case must be scrutinized by applying this "hypothetical leader" test.
The military services demand a regard for authority by juniors towards their seniors which experience has shown is enhanced by the observance of decorum, tradition, custom, usage, and conventions which are peculiar to the services alone. The unquestioned obedience mandated in time of battle rests on regard and respect for authority. This respect is lessened by the failure to observe niceties of military courtesy and other traditions and customs.
The Marine Corps cannot legally act to prevent marriages between service members. A marriage between Marines of differing grades will constitute fraternization when the impact of the marriage detracts or tends to detract from the respect due a senior, or is perceived by others to do so.
A marriage stemming from a previously existing improper relationship does not excuse those involved from responsibility for their activities prior to the marriage.
a. Non-punitive administrative remedies.
(1) Formal or informal counseling.
(2) Transfer of one or both parties.
(3) Fitness report comments.
b. Nonjudicial punishment (often followed, in the case of officers, by processing for administrative separation).
The responsibility for maintaining the customary and traditional standards of conduct lies with the senior. The line between acceptable conduct and fraternization will not be crossed unless the senior allows it to happen.
The leader must be careful to avoid even the perception of fraternization without destroying the traditional fraternal bond between Marines of all grades.