The general structure of the military is pyramidal, with the president of the United States acting as the commander-in-chief of the U.S. Armed Forces. The president's responsibilities include appointing top military officers and maintaining the nation's military strength.

The secretary of defense is an appointed position usually awarded to a civilian. He or she is a member of the president's cabinet, presiding over the Department of Defense and directing the operations of all military branches. The joint chiefs of staff, the senior commanders of the different services, work with the secretary of defense to advise the president on military matters. (The Coast Guard is now a service of the Department of Homeland Security; its commander is not a member of the joint chiefs.)

Together under the auspices of the Department of Defense, the individual services—the Army, Navy, Air Force, Marine Corps, and Coast Guard—comprise the armed forces. In 2019, more than 1.3 million people were serving in the armed forces, with 800,818 serving in the Reserve branches. (Reservists generally devote one weekend a month and two weeks a year to military service and may be called up for full-time duty whenever necessary.) The goals of all five branches are similar: the defense and protection of U.S. citizens, territory, and interests at home and around the world. Each service has a different role to play, however.

The Army is the senior service. It is traditionally known as the branch that fights on land. Most of the United States' more than 22.3 million living veterans served in the Army, and the Army continues to be the largest of the services in total recruits, with 468,783 soldiers on active duty in 2019.

The Navy, more than any of the other services, has a special way of life. Guided by traditions of the sea, it is in many ways more of a closed society than the other services. Its officers and enlisted people work and live together at sea for long periods, a lifestyle that demands close attention to duties and teamwork. Ships and aircraft units visit many parts of the world. It can be an unusual and wonderful life, and strongly appealing to many who are looking for a different and exciting type of career. The Navy had about 330,949 personnel on active duty in 2019, an increase over 322,928 active-duty personnel in 2016.

The Air Force, the newest of all the services, is highly technical and appeals to those interested in aviation and mechanical trades. In 2019, there were 327,039 officers and airmen on active duty in the Air Force, which was an increase compared to the 307,845 personnel on active duty in 2016.

The Marine Corps operates on land and sea, and Marines usually form the advance troops in military operations. The corps is closely associated with the Navy and, like the Navy, prides itself on meeting the highest possible standards in training, military bearing, and discipline. Apart from more military duties, Marines provide security on navy property and guard U.S. embassies and consulates around the world. There were approximately 186,814 Marines on active duty in 2019.

In 2019, there were approximately 41,250 individuals serving in the Coast Guard. The Coast Guard is the smallest of the military services, and, as such, offers unique opportunities. It is responsible largely for the enforcement of maritime law, but is perhaps most well known for its involvement in search-and-rescue efforts, aiding those in distress at sea. Although opportunities exist for overseas assignments, most duties in the Coast Guard are related to the waters and shores of the United States.

Positions in the military fall under two broad occupational categories: enlisted personnel and officers. Enlisted personnel execute the daily operations of the military, and are considered noncommissioned officers. Commissioned officers function as managers of the military, overseeing the work of the enlisted personnel.

In addition, both the Army and Navy maintain a third classification of skilled experts called warrant officers. Enlisted soldiers or civilians who demonstrate technical and tactical ability in any one of several dozen occupational specialties may qualify as a warrant officer. Warrant officers are highly specialized and gain additional expertise by operating, maintaining, and managing the services' equipment, support activities, and technical systems throughout their careers. Specialties include, but are not limited to, missile systems, military intelligence, telecommunications, legal administration, and personnel.

A broad general difference between the requirements for enlisted personnel and officers is academic preparation. The service branches accept applicants of varying ages and educational backgrounds, although officers are required to have college degrees and enlisted people are not. Those who intend to serve as enlisted personnel should finish high school and then enlist. High school graduates are more likely to be successful in the military than nongraduates, and the services accept few applicants without a high school diploma. All service applicants must take the Armed Services Vocational Aptitude Battery (ASVAB) as a requirement for enlistment.

All service personnel receive special training in military skills. Those who want to rise in the ranks have the opportunity to attend school or undertake independent study and will be rewarded with advancement. Military education in many instances is related to civilian occupations, an added incentive for those who later decide not to make a career of military service.

While many recruits enter the armed forces immediately after graduating from high school, the military uses every opportunity to advance the education of its recruits. Frequently, service members in both categories, both officers and enlisted men and women, obtain undergraduate and advanced degrees on their own initiative while in the service. The range of educational possibilities is diverse and often exciting, and financial help for study at outside institutions is readily available. You can learn to operate the engineering equipment of an aircraft carrier or, with appropriate academic qualifications, proceed through medical training to become a military physician. With a serious sense of commitment and a great deal of rigorous preparation, you even can join the Navy's SEALS program, or "get jets," and become a member of the Blue Angels.

Each military branch has nine enlisted grades and 10 officer designations. The names of ranks vary among the services. This is why a simple numbering system has been adopted to denote rank. Promotion depends on ability, the number of years served, and the length of time since the last promotion. On average, a diligent enlisted person can expect to earn one of the middle noncommissioned or petty officer ratings; some officers can expect to reach lieutenant colonel or commander. Outstanding individuals advance beyond those levels.

The pay for the equivalent grades in all services is the same. It starts comparatively low for new recruits but increases on a fairly regular schedule to a more substantial salary for top officers and enlisted people. Congress sets the pay scales after hearing the recommendations of the president. In addition to basic pay, hazardous duty pay may be earned by enlisted personnel who frequently and regularly participate in combat. Other special allowances include special duty pay and foreign duty pay.

The services also supply without charge many basic necessities such as food, shelter, and health care, which must be paid out of pocket in most civilian positions. Military men and women receive a number of additional benefits. They include access to recreational facilities, free medical and dental care, schools for dependents, financial advice, legal assistance, and religious support.

Military people may apply for retirement after 20 years of service. Generally, people retiring from military service will receive 40 percent of the average of the highest three years of their base pay. This rises incrementally, reaching 75 percent of the average of the highest three years of base pay after 30 years of service. The widow or widower of a service member who died on active duty or after a service-connected disability discharge will receive, for life or until remarriage, a monthly payment computed on the basis of the deceased spouse's rank. The surviving spouse also receives disability insurance.

At about age 40, a person is still in the prime of life for most work, and although the retirement pay is comparatively good, military retirees generally choose to start new careers in civilian life. Military training usually has prepared a person for a related trade or profession, and many military people look forward to early retirement. They view it as an excellent opportunity to take a civilian job and keep the financial cushion of military retirement pay. Others, of course, prefer to stay in the service longer, or perhaps for their entire working lives; generally speaking, only the more senior service members have that opportunity. Even in retirement, service people are subject to recall in times of national emergency.