Appropriate Times to Wear the Army Saber
AR 670-1 is silent on the wear of the saber (or NCO sword). The only official document that we know of that depicts the wear of the saber is FM 3-21.5, Drill and Ceremonies, in which there is a figure of an officer wearing the saber in Class A. The Old Guard also wears the saber with dress blues.
In practice today, Soldiers are wearing the Army saber or sword more frequently on occasions of ceremony ... weddings, funerals, formal dinners, formal receptions, unit dining-in functions, retirements (to a lesser extent), etc.
The saber is worn with the ceremonial belt when used with the Army Service Uniform (ASU). Officers will wear their branch-colored ceremonial belt and NCO's will wear the Enlisted belt
The wear of the saber with the mess uniform is unusual and is the most unclear, though some Soldiers today choose to do it. Accordingly, we typically recommend that the Soldier wear the cummerbund over the belt. For this reason, we would recommend the ceremonial belt because its buckle offers less of a bulge in the front under the cummerbund than a leather belt. Keep in mind, however, that the belt would be largely unseen under the cummerbund unless the officer removes his or her jacket for some reason. Just about any belt that offers a low profile under the cummerbund would work, although there is some risk of the belt being seen from the back if the Soldiers bends over, etc.
Also, when wearing the mess or the dress blue uniforms under arms, the paragraph in AR 670-1 stating that the wear of headgear is optional after retreat would not apply. One should always wear cover when under arms outside and when under arms inside while acting in an official capacity (directed by commander, indoor ceremonial events, etc.).