Throughout the Vietnam War, more than 170,000 Americans — including Muhammad Ali —registered for conscientious objector status. Citing ethical, moral or religious grounds, conscientious objectors either oppose all military service or oppose service that requires them to use a weapon.
Must provide documentation: A registrant has to appear before a local military board and either provide written documentation or have others who can attest to his beliefs, such as a lawyer or religious adviser, provide additional evidence.
Religious beliefs aren't required: The decision to eschew military service can be based on ethical or moral beliefs, but not on politics or self-interest.
Claims are handled on an individual basis: According to the Department of Defense, requests for conscientious objector status are determined by the local military board because there is no across-the-board standard.
Alternative services: A person opposed to any form of military service will be assigned to civilian roles such as health care or education that support national security. Those who consent to serve in the military as non-combatants are assigned duties that don't require weapons.
Source: US. Selective Service