Final answer:
The Secretary of the Navy or the Commanding General of the Marine Corps has the authority to revoke a Navy and Marine Corps Achievement Medal (NAM) after presentation for specific reasons such as misconduct or discreditable actions.
Step-by-step explanation:
The authority to revoke a Navy and Marine Corps Achievement Medal (NAM) after presentation lies with the Secretary of the Navy or the Commanding General of the Marine Corps.
Typically, the Secretary of the Navy has the authority to revoke the medal for reasons such as misconduct, discreditable actions, or other circumstances that warrant such action.
It is important to note that revoking a Navy and Marine Corps Achievement Medal after presentation is a rare occurrence and is typically only done in exceptional circumstances.