U.S. Military 101 - Army, Navy, Air Force, Marines

The Basics of the United States Military (All Branches)

Branches of Military
••• Army, Navy, AF, USMC.

Our present military organizational structure is a result of the National Security Act of 1947. This is the same act that created the United States Air Force, and restructured the "War Department" into the "Department of Defense."

The Department of Defense

The Department of Defense is headed by a civilian; the Secretary of Defense, who is appointed by the President of the United States and approved by the Senate. Under the Secretary of Defense, there are three military departments: The Department of the Army, the Department of the Air Force, and the Department of the Navy. Each of these military departments are also headed up by civilians; the Secretary of the Army, the Secretary of the Air Force, and the Secretary of the Navy. These "service secretaries" are also appointed by the President.

There are five military branches: The Army, Air Force, Navy, Marine Corps, and Coast Guard. The Army is commanded by a four-star general, known as the Army Chief of Staff. The Army Chief of Staff reports to the Secretary of the Army (for most matters). The top military member in the Air Force is the Air Force Chief of Staff. This four-star general reports (for most matters) to the Secretary of the Air Force. The Navy is commanded by a four-star admiral, called the Chief of Naval Operations. The Marines are commanded by a 4-star general called the Commandant of the Marine Corps.

Both the Chief of Naval Operations and the Marine Corps Commandant report (for most matters) to the Secretary of the Navy. So yes, the Marine Corps is technically part of the Navy.

These four "flag officers" also make up a group called the Joint Chiefs of Staff (JSC). The Joint Chiefs of Staff comprise the four Service Chiefs, the Vice Chairman of the Joint Chiefs of Staff, and the Chairman of the Joint Chiefs of Staff. The Chairman is nominated by the President and approved by the Senate (as are other general and flag officer positions). For operational matters (such as war or conflict), the JCS by-passes the individual service secretaries and report directly to the Secretary of Defense and the President.

Functions of the Five Branches of the Military


The United States Army is the main ground-force of the United States. The Army's main function is to protect and defend the United States (and its interests) by way of ground troops, armor (tanks), artillery, attack helicopters, tactical nuclear weapons, etc. The Army is the oldest U.S. Military service, officially established by the Continental Congress on June 14, 1775. The Army is also the largest U.S. Military Service. The Army is supported by two Reserve Forces which can be tapped for trained personnel and equipment during times of need: The Army Reserves, and the Army National Guard.

The primary difference between the two is that the Reserves are "owned" and managed by the federal government, and each state "owns" it's own National Guard. However, the President of the United States or the Secretary of Defense can "activate" state National Guard members into Federal military service during times of need. Active duty population: 471,000.  

Air Force

The Air Force is the youngest military service. Prior to 1947, the Air Force was a separate Corps of the Army. The primary mission of the Army Air Corps was to support Army ground forces. However, World War II showed that air power had much more potential than simply supporting ground troops, so the Air Force was established as a separate service. The primary mission of the Air Force is to defend the United States (and its interests) through exploitation of air and space. To accomplish this mission, the Air Force operates fighter aircraft, tanker aircraft, light and heavy bomber aircraft, transport aircraft, and helicopters (which are used mainly for rescue of downed aircrew, and special operations missions).

The Air Force is also responsible for all military satellites and controls all of our Nation's strategic nuclear ballistic missiles.  Like the Army, the active duty Air Force is supplemented by the Air Force Reserves, and the Air National Guard.  Active duty population: 322,000.


Like the Army, the Navy was officially established by the Continental Congress in 1775. The Navy's primary mission is to maintain the freedom of the seas. The Navy makes it possible for the United States to use the seas where and when our national interests require it. In addition, in times of conflict, the Navy helps to supplement Air Force air power. Navy aircraft carriers can often deploy to areas where fixed runways are impossible. An aircraft carrier usually carries about 80 aircraft. Most of these are fighters or fighter-bombers.

Additionally, Navy ships can attack land targets from miles away (with very heavy guns), and cruise missiles. Navy submarines (fast attack and ballistic missile subs) allow stealth attacks on our enemies from right off their shores. The Navy is also primarily responsible for transporting Marines to areas of conflict. The active duty Navy has about 54,000 officers, and 324,000 enlisted personnel. The Navy is supported in times of need by the Naval Reserves. However, unlike the Army and Air Force, there is no Naval National Guard (although a few states have established "Naval Militias.")

Active duty population: 324,000

Marine Corps

Marines specialize in amphibious operations. In other words, their primary specialty is to assault, capture, and control "beach heads," which then provide a route to attack the enemy from almost any direction. The Marines were officially established on 10 November 1775 by the Continental Congress to act as a landing force for the United States Navy. In 1798, however, Congress established the Marine Corps as a separate service. While amphibious operations are their primary specialty, in recent years, the Marines have expanded other ground-combat operations, as well.

The Marines are generally a "lighter" force when compared to the Army, so they can generally be deployed quickly (although the Army has been making great strides in "rapid deployment" in the past few years). For combat operations, the Marines like to be self-sufficient as much as possible so they also have their own air power, consisting primarily of fighter and fighter/bomber aircraft and attack helicopters. Even so, the Marines use the Navy for much of their logistical and administrative support.

For example, there are no doctors, nurses, or enlisted medics in the Marine Corps. Even medics that accompany the Marines into combat are specially-trained Navy medics. 

Active duty population: 184,000

Total 2017 Population: 1.4 million active duty Army, Navy, Air Force, Marines

Coast Guard

The United States Coast Guard was originally established as the Revenue Cutter Service in 1790. In 1915, it was reformed as the United States Coast Guard, under the Treasury Department. In 1967, the Coast Guard was transferred to the Department of Transportation. Legislation passed in 2002 transferred the Coast Guard to the Department of Homeland Security. In peacetime, the Coast Guard is primarily concerned with law enforcement, boating safety, sea rescue, and illegal immigration control. However, the President of the United States can transfer part or all of the Coast Guard to the Department of the Navy in times of conflict.

The Coast Guard consists of ships, boats, aircraft and shore stations that conduct a variety of missions. The Coast Guard is the smallest military service, with about 7,000 officers and 29,000 enlisted on active duty. The Coast Guard is also supported by the Coast Guard Reserves, and a volunteer "Coast Guard Auxiliary" in times of need.

The Coast Guard is considered a military service, because, during times of war or conflict, the President of the United States can transfer any or all assets of the Coast Guard to the Department of the Navy. In fact, this has been done in almost every single conflict that the United States have ever been involved in. The Coast Guard is commanded by a 4-star admiral, known as the Coast Guard Commandant.

Active duty population: 36,000, but with Reserves (7,000) and Auxiliary (29,000)

Enlisted personnel

Enlisted members are the "backbone" of the military. They perform the primary jobs that need to be done. Enlisted members are "specialists." They are trained to perform specific specialties in the military. As enlisted personnel progress up the ranks (there are nine enlisted ranks), they assume more responsibility, and provide direct supervision to their subordinates.

Enlisted personnel in certain grades have special status. In the Army, Air Force, and Marine Corps, this status is known as "Noncommissioned Officer status, or "NCO." In the Navy and Coast Guard, such enlisted are known as "Petty Officers." In the Marine Corps, NCO status begins at the grade of E-4 (Corporal).

In the Army and Air Force, enlisted personnel in the grades of E-5 through E-9 are NCOs. However, some Army E-4s are laterally promoted to "corporal," and are considered NCOs.

Also in the Army and Air Force, personnel in the grades of E-7 to E-9 are known as "Senior NCOs."

In the Marine Corps, those in the grades of E-6 through E-9 are known as "Staff NCOs."

In the Navy/Coast Guard, Petty Officers are those in the grades of E-4 through E-9. Those in the grades of E-7 to E-9 are known as "Chief Petty Officers."

Warrant Officers

 Warrant Officers are very highly-trained specialists. This is where they differ from commissioned officers. Unlike commissioned officers, warrant officers remain in their primary specialty to provide specialized knowledge, instruction, and leadership to enlisted members and commissioned officers alike.

With few exceptions, one must be an enlisted member with several years of experience, recommended by their commander, and pass a selection board to become a warrant officer. The Air Force is the only service which does not have warrant officers. The Air Force eliminated their warrant officer positions when Congress created the grades of E-8 and E-9 in the late 60s. The other services elected to retain the warrant ranks, and shifted the emphasis from a promotion process for E-7s to a highly selective system for highly-skilled technicians.

There are five separate warrant ranks. Warrant Officers outrank all enlisted members.

Commissioned Officers

Commissioned Officers are the "top brass." Their primary function is to provide overall management and leadership in their area of responsibility. Unlike enlisted members and warrant officers, commissioned officers do not specialize as much (with certain exceptions such as pilots, doctors, nurses, and lawyers). Let's take for example, an infantry officer. An enlisted member in the Infantry Branch will have a specific infantry specialty, such as infantryman (MOS 11B), or indirect fire infantryman (11C).

Unless that enlisted member retrains, he will remain an 11B or 11C for his career. The officer, however, is designated to the "Infantry Branch." He can start his career in charge of a light infantry platoon, then may move on to be in charge of a mortar platoon, then later in his career he may move on to become a company commander, commanding various types of infantry troops. As he moves up the ranks, he gets more and more experience in the different areas of his branch, and is responsible for commanding more and more troops.

All of this has the primary purpose of (ultimately) generating an experienced officer who can command an entire infantry battalion or division.

Commissioned Officers must have a minimum of a four-year bachelor's degree. As they move up the ranks, if they want to get promoted, they will have to earn a masters degree. Commissioned Officers are commissioned through specific commissioning programs, such as one of the military academies (West Point, Naval Academy, Air Force Academy, Coast Guard Academy), ROTC (Reserve Officer Training Corps, or OCS (Officer Candidate School), called OTS (Officer Training School) for the Air Force.

There are also two basic "types" of commissioned officers: Line and Non-Line. A Non-line officer is a non-combat specialist which includes medical officers (doctors and nurses), lawyers, and chaplains. Non-Line officers cannot command combat troops as they are specialists and have different jobs and responsibilities. 

Conclusion / Comparison to Corporate Professions

Think of the enlisted member as the worker in a civilian company. The enlisted are the ones who are hands-on and perform the job. Within the "worker group," NCOs (Army, Air Force, and Marines) and Petty Officers (Navy and Coast Guard) are the supervisors. They perform the job, but also provide direct supervision to the other workers. Senior NCOs (Army Air Force and Marines) and Chief Petty Officers (Navy and Coast Guard) are assistant managers who came up through the ranks of the corporation. They are valuable as managers because of their many years of experience, but will never make it to the Board of Directors.

Commissioned officers are the managers of the company. They have broad areas of responsibility for the management, organization, and efficiency of various departments of the corporation. Senior commissioned officers (generals and admirals) are the board of directors. Warrant Officers can be thought of as the experienced technical specialists that the company hired to perform highly-specialized functions.