| Class | Categories (1948–1975) |
| 1-A | Available for unrestricted military service |
| 1-A-O | Conscientious objector available for noncombatant military service only |
| 1-C | Member of the Armed Forces of the United States, the National Oceanic and Atmospheric Administration, or the Public Health Service. Enlisted (Enl.): member who volunteered for service. Inducted (Ind.): member who was conscripted into service. Discharged (Dis.): member released after completing service; later changed to Class 4-A. Separated (Sep.): member released before completing service; may be recalled to service if their status has changed |
| 1-D | Members of a reserve component (reserves or National Guard), students taking military training (service academy, senior military college, or ROTC), or accepted aviation cadet applicants (1942–1975) |
| 1-D-D | Deferment for certain members of a reserve component or student taking military training |
| 1-D-E | Exemption of certain members of a reserve component or student taking military training |
| 1-H | Registrant not currently subject to processing for induction or alternative service Within the cessation of registrant processing in 1976, all registrants (except for a few alleged violators of the Military Selective Service Act) were classified 1-H regardless of any previous classification. |
| 1-O | Conscientious objector to all military service. A registrant must establish to the satisfaction of the board that his request for exemption from combatant and noncombatant military training and service in the Armed Forces is based upon moral, ethical or religious beliefs which play a significant role in his life and that his objection to participation in war is not confined to a particular war. The registrant is still required to serve in civilian alternative service. |
| 1-O-S | Conscientious objector to all military service (separated). A registrant separated from the Armed Forces due to objection to participation in both combatant and noncombatant training and service in the Armed Forces. The registrant is still required to serve in civilian alternative service. |
| 1-S (H) | Student deferred by statute (high school). Induction can be deferred either until graduation or until reaching the age of 20. |
| 1-S (C) | Student deferred by statute (college). Induction can be deferred either to the end of the student's current semester if an undergraduate or until the end of the academic year if a senior. |
| 1-W | Conscientious objector currently performing assigned alternative service. They must serve for a set period of time equal to their owed national service (currently 24 consecutive months). |
| 1-W-R | (Released) Conscientious objector who satisfactorily completed their service. This was later changed to Class 4-W. |
| mw- } }1-Y | Registrant qualified for service only in time of war or national emergency The 1-Y classification was abolished 10 December 1971. Local boards were subsequently instructed to reclassify all 1-Y registrants by administrative action. |
| 2-A | Registrant deferred because of essential civilian non-agricultural occupation. Also includes deferments due to full-time study or training in an essential trade or profession at a trade school, community or junior college, or an approved apprenticeship program |
| 2-B | Registrant deferred because of occupation in a war industry or a trade or profession considered essential to national defense: (defense contractor or reserved occupation). This exemption was discontinued in 1951. |
| 2-C | Registrant deferred because of agricultural occupation |
| 2-D | Registrant is a divinity student attending an accredited theological or divinity school to be prepared for the ministry. Deferment lasted either until graduation or until the registrant reached the age of 24. Exemption was created in December 1971. Previously considered part of Class 4-D |
| 2-S | Registrant deferred because of collegiate study. Deferment lasted either until graduation or until the registrant reached the age of 24. Exemption was discontinued in December 1971.It previously also deferred graduate students studying medicine, dentistry, veterinary medicine, osteopathic medicine, and optometry, and graduate students in their fifth year of continuous study toward a doctoral degree. The exemption for graduate and doctoral students was discontinued in 1967. |
| 3-A | Registrant deferred because of hardship to dependents |
| 3-A-S | Registrant deferred because of hardship to dependents (separated). Current serving member or registrant undergoing induction separated from military service due to a change in family status. The registrant's deferment can last no longer than six months, after which they may re-file if the hardship continues to exist. |
| 4-A | Registrant who has completed military service |
| 4-A-A | Registrant who has performed military service for a foreign nation |
| 4-B | Official deferred by law |
| 4-C | Alien or dual national |
| 4-D | Minister of religion, formally ordained by a recognized religion, and serving as a full-time minister with a church and congregation |
| 4-E | Conscientious objector opposed to both combatant and noncombatant training and service. Alternative service in lieu of induction may still be required. Created in 1948; changed to Class 1-O in 1951 |
| 4-F | Registrant not acceptable for military service. To be eligible for Class 4-F, a registrant must have been found not qualified for service in the Armed Forces by an MEPS under the established physical, mental, or moral standards. Future standards of physical fitness came from AR 40-501. |
| 4-G | Registrant exempted from service because of the death of a parent or sibling while serving in the Armed Forces or whose parent or sibling has Prisoner of War or Missing In Action status |
| 4-T | Treaty alien |
| 4-W | Conscientious objector who has fully and satisfactorily completed alternative service in lieu of induction |
| 5-A | Registrant who is over either the age of liability if a deferment had not been taken (currently 26 years or older) or (where applicable) the age of liability if a deferment with extended liability had been taken (currently 35 years or older) |
