This article includes a list of general references, but it lacks sufficient corresponding inline citations .(May 2008)
A United States military occupation code, or a military occupational specialty code (MOS code), is a nine-character code used in the United States Army and United States Marine Corps to identify a specific job. In the United States Air Force, a system of Air Force Specialty Codes (AFSC) is used. In the United States Navy, a system of naval ratings and designators are used along with the Navy Enlisted Classification (NEC) system. A system of ratings is also used in the United States Coast Guard.
Since an individual can obtain multiple job specialties, a duty military occupational specialty (DMOS) is used to identify what their primary job function is at any given time. An individual must complete and pass all required training for their military occupational specialty qualification (MOSQ).
Originally, the four-digit MOS code mostly listed the recruit's civilian profession. This was to aid in classifying what military job they could be assigned. With so many recruits being processed, identifying any semi-skilled or skilled civilian tradesmen made it easier to match them with the right military job. There was an additional list of military trades and trainings added so a trained soldier could be assigned to the right unit. There were no grouping of similar trades together, making it hard for someone to know the meaning of an MOS code without a manual.
The MOS system now had three to five digits. The first four-digit code number indicated the soldier's job; the first two digits were the field code, the third digit was the sub-specialty and the fourth code number (separated by a period) was the job title. A fifth code digit was for the soldier's special qualification identifier (SQI) digit, which indicated what specialized training the soldier had. If the soldier did not have an SQI, the digit was listed as "0" or was omitted. The codes for the civilian trades were removed as unnecessary.
In 1965 the system was revamped. There were completely different codes for enlisted / non-commissioned officers, warrant officers, and commissioned officers.
Enlisted and NCO personnel had a five-symbol code. The first four code symbols were made up of a two-digit code for the career field, a letter code for the field specialty, and a number code (1 to 5) indicating level of instruction in their field specialty. The fifth code symbol was an SQI code letter indicating training in a special skill (the letter "O" indicating that the soldier had no SQI). An exception to the 5-symbol rule was made for an SQI which indicated language fluency. In this case, 7 symbols were used, with "L" as the language qualification indicator, followed by two characters indicating the specific language.
Warrant officers also had a five-symbol code but it was different. The first three numbers were the career field, then a letter code for the field specialty, and ended in the SQI code letter.
Officers had a four-digit code number for their career field and specialty. Officers with a special qualification also had an SQI code number prefix to their MOS rather than a code letter suffix. Officers without a special qualification had no prefix number.
In 1983, there was a reform of this system. Some of the field code numbers were changed and the MOS codes were streamlined.
Warrant officers and officers received the same career field codes as enlisted and NCO personnel and ended in the same SQI letter codes. Warrant officers received a five-symbol MOS consisting of a four-symbol field specialty code consisting of the two-digit field code, a one-digit sub-field code number (usually "0"), the field specialty code letter, and followed by the SQI code letter. Officers now had a four-symbol alphanumeric MOS. It consisted of the three-symbol field specialty code of two numbers and a specialty code letter and ended in the SQI letter code.
The field code "18" was created for US Army Special Forces, which are now considered part of the regular US Army. Previously they had been considered a layer between the intelligence services and the army. The 18A was for special forces officers and 180A was for special forces warrant officers. The 18X was for special forces candidates who had not yet passed the "Q" course. The "A" team leaders had to be captains instead of lieutenants and were rotated to conventional postings.
Certain field specialty code letters were reserved. The "X" was for recruits or candidates who have pre-selected a career field but had not graduated from AIT. The "Z" is for senior NCOs of E8 or E9 grade. The "A" is for officers and warrant officers in a general capacity. Specialist officers and warrant officers have other field code letters reserved for them.
The list of US Army military occupational specialty codes is published on the United States Army Human Resources Command (HRC) PAMXXI website. 
The MOS code (MOSC), consisting of nine characters, provides more information than a soldier's MOS. It is used by automated management systems and reports. The MOSC is used with active and reserve records, reports, authorization documents, and other personnel management systems.
The elements of the MOSC are as follows:
When an enlisted soldier is promoted from sergeant first class to master sergeant in most career types, that soldier will be reclassified administratively to the "senior sergeant" of their career management field. For example, a combat engineer (MOS 12B, part of CMF 12) is promoted from sergeant first class to master sergeant. That soldier is reclassified administratively from MOS 12B to MOS 12Z "senior engineer sergeant"). An example of when this conversion occurs at the MSG to SGM level is the 68 (formerly the 91) CMF. In this case, the soldier becomes a 68Z at the SGM level, not the MSG level. When promoted from master sergeant or first sergeant or sergeant major to command sergeant major, that soldier will be reclassified administratively from their previous "senior sergeant" MOS to the MOS 00Z (zero-zero-zulu), "command sergeant major". Some MOS do not change though, for example 25U starts out as 25U1O (E1-E4), and advances though 25U2O (E5/SGT), 25U3O (E6/SSG), 25U4O (E7/SFC), and 25U5O (E8, E9/MSG, 1SG, SGM, CSM)
Warrant officers are sometimes specialized technicians and systems managers, and were not originally assigned to traditional arms or services of the Army. Approximately 50% of warrant officers are aviators  (aircraft pilots, rotary wing and fixed wing), and can be appointed directly from civilian life  or within the service, regardless of previous enlisted MOS. The remaining 50% are technicians appointed from experienced enlisted soldiers and NCOs in a "feeder"  MOS directly related to the warrant officer MOS. 
During 2004, all army warrant officers began wearing the insignia of their specialty's proponent branch rather than the 83-year-old "Eagle Rising" distinctive warrant officer insignia.  The following year, a revision of commissioned officer professional development and career management  integrated warrant officer career development with the officer career development model. In practice, warrant officer MOSC are very similar to enlisted codes except they begin with three digits instead of two before the first letter, and do not have a "skill level" identifier. They are then followed by the SQI, ASI, and SLI as an enlisted MOS would be.
Commissioned officers' occupational codes are structured somewhat differently. A newly commissioned army officer first receives a "career branch". This is similar to the career management field of the enlisted personnel. Career branch numbers range from 11 to 92. For example: 13 for field artillery, 19 for armor/armored cavalry and 92 for quartermaster. Within each occupational field, there are usually several codes available. Within armor (branch 19) there are three specialties available: 19A (armor, general), 19B (armor), and 19C (cavalry). After an officer's fifth or sixth year of service, he or she may receive a "functional area" designation. More specific than a career branch, this is a specific skill set in which the officer is proficient. For example, an artillery officer who has had schooling in communications and public speaking could end up with a functional area in public affairs (FA46).
The U.S. Marine Corps begins by separating all jobs into "occupational fields" (OccFld), in which no distinction is made between officers and enlisted Marines. The fields are numbered from 01 to 99 and include general categories (intelligence, infantry, logistics, public affairs, ordnance, etc.) under which specific jobs fall. 
Each field contains multiple MOS's, each designated by a four-digit numerical indicator and a job title. Most fields have at least one "basic MOS" for enlisted, and one "basic MOS" for officers, who have yet to be fully trained in any other MOS within that field. Upon completion of required training, the Marine is reclassified from their "basic MOS" to a "primary MOS" in which Marines generally will serve the remainder of their careers, be assigned, seek promotion, and be retained.
Additionally, many fields have specialty MOS's, such as "necessary MOS's," for which there may be varying prerequisites and assignment criterion. Marines do not compete for promotion or retention based on their NMOS, only their PMOS (or basic MOS, for those who have yet to complete training for a PMOS). A Marine who earns an NMOS retains it in their service records as an additional MOS beyond their PMOS, and multiple NMOS's (and PMOS's, in some cases) may be earned showing additional skills.
For example, the infantry field (03) has multiple enlisted classifications:
Each of the jobs have authorized ranks associated with them. For example, anyone ranking from private to sergeant can be a rifleman (0311), but only Marines ranking from staff sergeant to gunnery sergeant can be an infantry unit leader (0369).
Duties and tasks are identified by rank because the Marine Corps MOS system is designed around the belief that increased duties and tasks accompany promotions. The first two digits designate the field and, the last two digits identify the promotional channel and specialty.
For example, the MOS 0311 indicates that it is in occupational field 03 (infantry) and designates the "rifleman" (11) MOS. For warrant officers, the MOS 2305 indicates that it is in occupational field 23 (ammunition and explosive ordnance disposal) and designates the "explosive ordnance disposal officer" (05) MOS. For officers, the MOS 0802 indicates that it is in occupational field 08 (field artillery) and designates the "field artillery officer" (02) MOS.
On September 29, 2016, the Navy announced it would "modernize" all rating titles for Sailors with a new classification system that would move towards occupational specialty codes similar to how the other services operate.
Former Master Chief Petty Officer of the Navy Michael Stevens led the controversial review earlier this year for the Secretary of the Navy on behalf of Chief of Naval Operations, Admiral John Richardson.
Initially, the Navy Rating Modernization System eliminated all rating titles. The former Master Chief Petty Officer of the Navy, Steven S. Giordano, said:
"Sailors would no longer be called, 'Yeoman Second Class' or YN2, for example," he said. "Instead they will be 'Second Class Petty Officer, or 'Petty Officer.' However, Sailors' ranks will not change: an E-7 will remain a Chief Petty Officer and an E-3 will remain a Seaman. Additionally, there will no longer be a distinction between 'airman, fireman and seaman.'"
The fleet at large did not respond to this favorably. As a result, Admiral Richardson rescinded this change on December, 21, 2016, restoring all rating titles. 
However, the plan retains the goal of producing sailors with more than one NOS, which might give them a broader range of professional experience and expertise and will be grouped under career fields that will enable flexibility to move between occupational specialties within the fields and will be tied to training and qualifications.
The transformation will occur in phases over a multi-year period and the Chief of Naval Personnel will lead the implementation efforts
The United States Navy has not released its NOS details yet and has not changed "designators" for officers.
The Navy indicates its "ratings" by a two or three character code based on the actual name of the rating. These range from ABE (aviation boatswain's mate - equipment) to YN (Yeoman). Each sailor and Chief Petty Officer wears a rating badge indicating their rating as part of their rate (rank) insignia on full dress and service dress uniforms.
The navy officer "designator" is similar to an MOS but is less complicated and has fewer categories. For example, a surface warfare officer with a regular commission has a designator of 1110; a reserve officer has an 1115 designator. A reserve surface warfare officer specializing in nuclear training (i.e., engineer on a carrier) has a designator of 1165N. Navy officers also have one or more three-character additional qualification designators (AQD) that reflect completion of requirements qualifying them in a specific warfare area or other specialization. In some senses this functions more like the MOS in other services. An officer with the naval aviator designator of 1310 might have an AQD of DV3, SH-60F carrier anti-submarine warfare helicopter pilot, or DB4, F-14 fighter pilot. An officer designated 2100, medical corps officer (physician) may hold an AQD of 6CM, trauma surgeon, or 6AE, flight surgeon who is also a naval aviator. Some AQDs may be possessed by officers in any designator, such as BT2, freefall parachutist, or BS1, shipboard Tomahawk strike officer. Navy officer designators and AQD codes may be found in NAVPERS 15839I, The Manual of Navy Officer Manpower and Personnel Classification.ip
The United States Coast Guard does not use the military occupational specialty concept either, instead dividing their occupational specialties into groups such as aviation, administrative and scientific, deck and weapons, and engineering and hull. Their rating system is very similar to the US Navy (e.g., BM, boatswain's mate).
The Coast Guard indicates its "ratings" by a two or three character code based on the actual name of the rating. These range from AMT (aviation maintenance technician) to YN (yeoman). Coast Guardsmen wear a rating badge indicating their rating as part of their rate (rank) insignia on full dress and service dress uniforms.
The Air Force utilizes a similar system, but titled "Air Force Specialty Code" (AFSC). Enlisted airmen have a five digit code, and officers have a four digit code.
Military ranks are a system of hierarchical relationships, within an armed forces, police, intelligence agencies or other institutions organized along military lines. The military rank system defines dominance, authority, and responsibility in a military hierarchy. It incorporates the principles of exercising power and authority into the military chain of command – the succession of commanders superior to subordinates through which command is exercised. The military chain of command constructs an important component for organized collective action.
A non-commissioned officer (NCO) is a military officer who has not pursued a commission. Non-commissioned officers usually earn their position of authority by promotion through the enlisted ranks. In contrast, commissioned officers usually enter directly from a military academy, officer candidate school (OCS), or officer training school (OTS) after receiving a post-secondary degree.
Sergeant is a rank in many uniformed organizations, principally military and policing forces. The alternative spelling, serjeant, is used in The Rifles and other units that draw their heritage from the British light infantry. Its origin is the Latin serviens, 'one who serves', through the French term sergeant.
Master gunnery sergeant (MGySgt) is the 9th and highest enlisted grade in the United States Marine Corps. Master gunnery sergeants are senior staff non-commissioned officers (SNCOs) with the pay grade of E-9, equivalent to sergeants major and the Sergeant Major of the Marine Corps.
The Career Counselor Badge is a military badge of the United States Army and Navy which was first established in the early 1970s. The badge recognizes those enlisted personnel who have been selected as promotion and career advancement coordinators, and Retention NCO's in the Army. The Navy and Army are the only branches of service to bestow a Career Counselor Badge.
A service number is an identification code used to identify a person within a large group. Service numbers are most often associated with the military; however, they may be used in civilian organizations as well. National identification numbers may be seen as types of service numbers.
A limited duty officer (LDO) is an officer in the United States Navy or United States Marine Corps who was selected for commissioning based on skill and expertise. They are the primary manpower source for technically specific billets not best suited for traditional Unrestricted Line, Restricted Line, or Staff Corps career path officers. Per Title 10, U.S. Code, an LDO is a permanent commissioned officer appointed under section 8139 in a permanent grade above chief warrant officer, W-5, and designated for limited duty.
Specialist is a military rank in some countries’ armed forces. In the United States Armed Forces, it is one of the four junior enlisted ranks in the U.S. Army, above private (PVT), private (PV2), and private first class and is equivalent in pay grade to corporal. In the U.S. Space Force it consists of the four junior enlisted ranks, prior to the rank of sergeant.
In the United States Armed Forces, the ranks of warrant officer are rated as officers above all non-commissioned officers, candidates, cadets, and midshipmen, but subordinate to the lowest officer grade of O‑1. This application differs from the Commonwealth of Nations and other militaries, where warrant officers are the most senior of the other ranks, equivalent to the U.S. Armed Forces grades of E‑8 and E‑9.
This is a list of rank insignia of the United States Marine Corps. Different styles of rank insignia are worn on different marine uniforms.
Public Affairs is a term for the formal offices of the branches of the United States Department of Defense whose purpose is to deal with the media and community issues. The term is also used for numerous media relations offices that are created by the U.S. military for more specific limited purposes. Public affairs offices are staffed by a combination of officers, enlisted personnel, civilian officials and contract professionals.
Combat arms is a collective name for troops within national armed forces which participate in direct tactical ground combat. In general, they include units that carry or employ a weapon system, such as infantry, cavalry, and artillery units. The use of multiple combat arms in mutually supporting ways is known as combined arms.
The infantry blue cord is a United States military decoration worn over the right shoulder of all infantry-qualified U.S. Army soldiers. It is a fourragere in light blue, specifically PMS 5415, worn under the right shoulder and under the right epaulette of a U.S. Army infantry soldier's Class A dress blue uniform jacket or Class B shirt. The cord is composed of a series of alternating left and right half knots that are tied around a leader cord to form a "Solomon bar".
The rank insignia of the federal armed forces of the Federal Republic of Germany indicate rank and branch of service in the German Army, German Air Force, or the German Navy.