The obligations of military employment are many. Full-time military employment normally requires a minimum period of service of several years; between two and six years is typical of armed forces in Australia, the UK and the US, for example, depending on role, branch, and rank.[19][20][21] Some armed forces allow a short discharge window, normally during training, when recruits may leave the armed force as of right.[22] Alternatively, part-time military employment, known as reserve service, allows a recruit to maintain a civilian job while training under military discipline at weekends; he or she may be called out to deploy on operations to supplement the full-time personnel complement. After leaving the armed forces, recruits may remain liable for compulsory return to full-time military employment in order to train or deploy on operations.[22][21]
As an adjective, military originally referred only to soldiers and soldiering, but it soon broadened to apply to land forces in general, and anything to do with their profession.[2] The names of both the Royal Military Academy (1741) and United States Military Academy (1802) reflect this. However, at about the time of the Napoleonic Wars, 'military' began to be used in reference to armed forces as a whole,[2] and in the 21st century expressions like 'military service', 'military intelligence', and 'military history' encompass naval and air force aspects. As such, it now connotes any activity performed by armed force personnel.
In the 2000s, women can serve on U.S. combat ships, including in command roles. They are permitted to serve on submarines.[37] Women can fly military aircraft and make up 2% of all pilots in the U.S. Military. In 2003, Major Kim Campbell was awarded the Distinguished Flying Cross for landing her combat damaged A-10 Thunderbolt II with no hydraulic control and only one functional engine after being struck by hostile fire over Baghdad.

Other training and auxiliary organizations of the Army, Marine Corps, Merchant Marine, Civil Air Patrol and Coast Guard Auxiliary, as in the preceding order. The CAP was constituted through the Administrative Order 9 of 1 December 1941 and operated under the U.S. Army Air Forces during World War II. The CAP became the official civilian auxiliary of the newly independent USAF with the enactment of Public Law 80-557 on 26 May 1948.

The military organization is characterized by a strict hierarchy divided by military rank, with ranks normally grouped (in descending order of authority) as officers (e.g. Colonel), non-commissioned officers (e.g. Sergeant), and personnel at the lowest rank (e.g. Private Soldier). While senior officers make strategic decisions, subordinated military personnel (soldiers, sailors, marines, or airmen) fulfil them. Although rank titles vary by military branch and country, the rank hierarchy is common to all state armed forces worldwide.

While considered part of the non-commissioned officer corps by law, senior non-commissioned officers (SNCOs) referred to as chief petty officers in the Navy and Coast Guard, or staff non-commissioned officers in the Marine Corps, perform duties more focused on leadership rather than technical expertise. Promotion to the SNCO ranks, E-7 through E-9 (E-6 through E-9 in the Marine Corps) is highly competitive. Personnel totals at the pay grades of E-8 and E-9 are limited by federal law to 2.5 percent and 1 percent of a service's enlisted force, respectively. SNCOs act as leaders of small units and as staff. Some SNCOs manage programs at headquarters level and a select few wield responsibility at the highest levels of the military structure. Most unit commanders have a SNCO as an enlisted advisor. All SNCOs are expected to mentor junior commissioned officers as well as the enlisted in their duty sections. The typical enlistee can expect to attain SNCO rank after 10 to 16 years of service.
Sergeant Leigh Ann Hester became the first woman to receive the Silver Star, the third-highest U.S. decoration for valor, for direct participation in combat. In Afghanistan, Monica Lin Brown was presented the Silver Star for shielding wounded soldiers with her body.[43] In March 2012, the U.S. military had two women, Ann E. Dunwoody and Janet C. Wolfenbarger, with the rank of four-star general.[44][45] In 2016, Air Force General Lori Robinson became the first female officer to command a major Unified Combatant Command (USNORTHCOM) in the history of the United States Armed Forces.[46]
In the Navy, the rank of Admiral of the Navy theoretically corresponds to that of General of the Armies, though it was never held by active-duty officers at the same time as persons who held the rank of Fleet Admiral. George Dewey is the only person to have ever held this rank. After the establishment of the rank of Fleet Admiral in 1944, the Department of the Navy specified that the rank of Fleet Admiral was to be junior to the rank of Admiral of the Navy. However, since Dewey died in 1917 before the establishment of the rank of Fleet Admiral, the six-star rank has not been totally confirmed.
Under current Department of Defense regulation, the various components of the U.S. Armed Forces have a set order of seniority. Examples of the use of this system include the display of service flags, placement of Soldiers, Marines, Sailors, Airmen and Coast Guardsmen in formation, etc. When the Coast Guard shall operate as part of the Department of the Navy, United States Coast Guard Academy cadets, the United States Coast Guard and the Coast Guard Reserve shall take precedence after United States Naval Academy midshipmen; the United States Navy; and Navy Reserve, respectively.[49]

The projected active duty end strength in the armed forces for fiscal year 2017 was 1,281,900 servicemembers,[4] with an additional 801,200 people in the seven reserve components.[4] It is an all-volunteer military, but conscription through the Selective Service System can be enacted at the President's request and Congress' approval. All males ages 18 through 25 who are living in the United States are required to register with the Selective Service for a potential future draft.

The AFQT (Armed Forces Qualifying Test) score is arguably the most important ASVAB score because it determines whether you’re eligible to join the military branch of your choice. Although the AFQT is often called the “overall ASVAB score,” that’s not quite correct, because it’s derived from only four subtests: Verbal Expression (VE), which is computed from the Paragraph Comprehension (PC) and Word Knowledge (WK) subtests, Arithmetic Reasoning (AR), and Math Knowledge (MK).