The United States Armed Forces  are the federal armed forces of the United States. They consist of the Army, Marine Corps, Navy, Air Force, and Coast Guard.  The President of the United States is the military's overall head, and helps form military policy with the U.S. Department of Defense (DoD), a federal executive department, acting as the principal organ by which military policy is carried out.
From the time of its inception, the military played a decisive role in the history of the United States. A sense of national unity and identity was forged as a result of victory in the First Barbary War and the Second Barbary War. Even so, the Founders were suspicious of a permanent military force. It played an important role in the American Civil War, where leading generals on both sides were picked from members of the United States military. Not until the outbreak of World War II did a large standing army become officially established. The National Security Act of 1947, adopted following World War II and during the Cold War's onset, created the modern U.S. military framework; the Act merged previously Cabinet-level Department of War and the Department of the Navy into the National Military Establishment (renamed the Department of Defense in 1949), headed by the Secretary of Defense; and created the Department of the Air Force and National Security Council.
The U.S. military is one of the largest militaries in terms of number of personnel. It draws its manpower from a large pool of paid volunteers; although conscription has been used in the past in various times of both war and peace, it has not been used since 1972. As of 2016, the United States spends about $580.3 billion annually to fund its military forces and Overseas Contingency Operations.  Put together, the United States constitutes roughly 39 percent of the world's military expenditures. For the period 2010–14, the Stockholm International Peace Research Institute (SIPRI) found that the United States was the world's largest exporter of major arms, accounting for 31 per cent of global shares. The United States was also the world's eighth largest importer of major weapons for the same period.  The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful equipment, and its widespread deployment of force around the world, including about 800 military bases in foreign locations. 
The DoD is headed by the Secretary of Defense, who is a civilian and Cabinet member. The Defense Secretary is second in the military's chain of command, just below the President, and serves as the principal assistant to the President in all DoD-related matters.  To coordinate military action with diplomacy, the President has an advisory National Security Council headed by a National Security Advisor. Both the President and Secretary of Defense are advised by a seven-member Joint Chiefs of Staff, which includes the head of each of the Defense Department's service branches as well as the chief of the National Guard Bureau. Leadership is provided by the Chairman of the Joint Chiefs of Staff and the Vice Chairman of the Joint Chiefs of Staff.  The Commandant of the Coast Guard is not a member of the Joint Chiefs of Staff.
All of the branches work together during operations and joint missions, under the Unified Combatant Commands, under the authority of the Secretary of Defense with the exception of the Coast Guard, which is under the administration of the Department of Homeland Security and receives its operational orders from the Secretary of Homeland Security. However, the Coast Guard may be transferred to the Department of the Navy by the President or Congress during a time of war.  All five armed services are among the seven uniformed services of the United States, the two others being the U.S. Public Health Service Commissioned Corps (under the Department of Health and Human Services) and the National Oceanic and Atmospheric Administration Commissioned Officer Corps (under the Department of Commerce).
Main article: Military budget of the United States
The United States has the world's largest military budget. In the fiscal year 2016, $580.3 billion in funding were enacted for the Department of Defense (DoD) and for "Overseas Contingency Operations" in the War on Terrorism.  Outside of direct DoD spending, the United States spends another $218 to $262 billion each year on other defense-related programs, such as Veterans Affairs, Homeland Security, nuclear weapons maintenance, and the State Department.
By service, $146.9 billion was allocated for the Army, $168.8 billion for the Navy and Marine Corps, $161.8 billion for the Air Force and $102.8 billion for defense-wide spending.  By function, $138.6 billion was requested for personnel, $244.4 billion for operations and maintenance, $118.9 billion for procurement, $69.0 billion for research and development, $1.3 billion for revolving and management funds, $6.9 billion for military construction, and $1.3 billion for family housing. 
In FY 2009, major defense programs saw continued funding:
$4.1 billion was requested for the next-generation fighter, F-22 Raptor, which was to roll out an additional 20 planes in 2009
$6.7 billion was requested for the F-35 Lightning II, which is still under development, but 16 planes were slated to be built
The Future Combat System program is expected to see $3.6 billion for its development.
A total of $12.3 billion was requested for missile defense, including Patriot CAP, PAC-3 and SBIRS-High.
Loren Thompson, a defense analyst with the Lexington Institute, has blamed the "vast sums of money" squandered on cutting-edge technology projects that were then canceled on shortsighted political operatives who lack a long-term perspective in setting requirements. The result is that the number of items bought under a given program are cut. The total development costs of the program are divided over fewer platforms, making the per-unit cost seem higher and so the numbers are cut again and again in a death spiral.  Although the United States was the world's biggest exporter of major weapons in 2010–14, the US was also the world's eight biggest importer during the same period. US arms imports increased by 21 per cent between 2005–2009 and 2010–14. 
Cost containment measures in the Patient Protection and Affordable Care Act and the Obama administration's energy policy will play a critical determining roles because health care and fuel costs are the two fastest-growing segments of the defense budget.  
The projected active duty end strength in the armed forces for FY 2016 was 1,301,300 people,  with an additional 811,000 people in the seven reserve components.  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 U.S. military is the world's second largest, after China's People's Liberation Army, and has troops deployed around the globe. From 1776 until September 2012, a total of 40 million people have served in the United States Armed Forces.  The FY 2017 DoD budget request  plan calls for an active duty end strength of 1,281,900, a decrease of 19,400 from the 2016 baseline as a result of decrements in the Army (15,000 fewer personnel) and Navy (4,400 fewer personnel) strength. The budget request also calls for a reserve component end strength of 801,200, a decrease of 9,800 personnel. As in most militaries, members of the U.S. military hold a rank, either that of officer, warrant, or enlisted, to determine seniority and eligibility for promotion. Those who have served are known as veterans. Rank names may be different between services, but they are matched to each other by their corresponding paygrade.  Officers who hold the same rank or paygrade are distinguished by their date of rank to determine seniority, while officers who serve in certain positions of office of importance set by law, outrank all other officers in active duty of the same rank and paygrade, regardless of their date of rank.  Currently, only one in four persons in the United States of the proper age meet the moral, academic and physical standards for military service. 
Personnel in each service
2010 Demographic Reports and end strengths for reserve components.    (should be updated using 2011 Demographic Reports  and Dec.2011 DMDC military personnel data  )
These numbers do not take into account the use of Private Military and Private Security Companies (PSCs). Quarterly PSC census reports are available for United States Central Command (USCENTCOM)'s area of operations—i.e., Iraq and Afghanistan.  As of March 2011, there were 18,971 private security contractor (PSC) personnel in Afghanistan working for DoD; in Iraq, there were 9,207 PSC personnel, down from a high of 15,279 in June 2009.  As of October 2012, in Afghanistan, there were 18,914 PSC personnel working for DoD; in Iraq, there were 2,116 PSC personnel.  The total number of DoD contractors in Iraq and Afghanistan was more than 137,400; reported PSCs were only a part of the number.
As of 31 December 2010, U.S. armed forces were stationed in 150 countries; the number of non-contingent deployments per country ranges from 1 in Suriname to over 50,000 in Germany.  Some of the largest deployments are: 103,700 in Afghanistan, 52,440 in Germany (see list), 35,688 in Japan (USFJ), 28,500 in South Korea (USFK), 9,660 inItaly, and 9,015 in the United Kingdom. These numbers change frequently due to the regular recall and deployment of units.
Altogether, 77,917 military personnel are located in Europe, 141 in the former Soviet Union, 47,236 in East Asia and the Pacific, 3,362 in North Africa, the Near East, and South Asia, 1,355 in sub-Saharan Africa and 1,941 in the Western Hemisphere excluding the United States itself.
Within the United States
Including U.S. territories and ships afloat within territorial waters
As of 31 December 2009, a total of 1,137,568 personnel were on active duty within the United States and its territories (including 84,461 afloat).  The vast majority (941,629 personnel) were stationed at bases within the contiguous United States. There were an additional 37,245 in Hawaii and 20,450 in Alaska; 84,461 were at sea, 2,972 in Guam, and 179 in Puerto Rico.
Types of personnel
Prospective service members are often recruited from high school or college, the target age ranges being 18–35 in the Army, 18–28 in the Marine Corps, 18–34 in the Navy, 18–39 in the Air Force, and 18–27 (up to age 32 if qualified for attending guaranteed "A" school) in the Coast Guard. With the permission of a parent or guardian, applicants can enlist at age 17 and participate in the Delayed Entry Program (DEP), in which the applicant is given the opportunity to participate in locally sponsored military activities, which can range from sports to competitions led by recruiters or other military liaisons (each recruiting station's DEP varies).
After enlistment, new recruits undergo basic training (also known as "boot camp" in the Marine Corps, Navy and Coast Guard), followed by schooling in their primary Military Occupational Specialty (MOS) or rating at any of the numerous training facilities around the world. Each branch conducts basic training differently. Marines send all non-infantry MOS's to an infantry skills course known as Marine Combat Training prior to their technical schools. Air Force Basic Military Training graduates attend Technical Training and are awarded an Air Force Specialty Code (AFSC) at the apprentice (3) skill level. All Army recruits undergo Basic Combat Training (BCT), followed byAdvanced Individual Training (AIT), with the exceptions of cavalry scouts, infantry, armor, combat engineers, and military police recruits who go to One Station Unit Training (OSUT), which combines BCT and AIT. The Navy sends its recruits to Recruit Training and then to "A" schools to earn a rating. The Coast Guard's recruits attend basic training and follow with an "A" school to earn a rating.
Initially, recruits without higher education or college degrees will hold the pay grade of E-1, and will be elevated to E-2 usually soon after basic training. Different services have different incentive programs for enlistees, such as higher initial ranks for college credit, being an Eagle Scout, and referring friends who go on to enlist as well. Participation in DEP is one way recruits can achieve rank before their departure to basic training.
There are several different authorized pay grade advancement requirements in each junior-enlisted rank category (E-1 to E-3), which differ by service. Enlistees in the Army can attain the initial pay grade of E-4 (specialist) with a four-year degree, but the highest initial pay grade is usually E-3 (members of the Army Band program can expect to enter service at the grade of E-4). Promotion through the junior enlisted ranks occurs after serving for a specified number of years (which, however, can be waived by the soldier's chain of command), a specified level of technical proficiency, or maintenance of good conduct. Promotion can be denied with reason.
With very few exceptions, becoming a non-commissioned officer (NCO) in the U.S. military is accomplished by progression through the lower enlisted ranks. However, unlike promotion through the lower enlisted tier, promotion to NCO is generally competitive. NCO ranks begin at E-4 or E-5, depending upon service, and are generally attained between three and six years of service. Junior NCOs function as first-line supervisors and squad leaders, training the junior enlisted in their duties and guiding their career advancement.
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.
Each of the five services employs a single Senior Enlisted Advisor at departmental level. This individual is the highest ranking enlisted member within that respective service and functions as the chief advisor to the service secretary, service chief of staff, and Congress on matters concerning the enlisted force. These individuals carry responsibilities and protocol requirements equivalent to three-star general and flag officers. They are as follows:
- Senior Enlisted Advisor to the Chairman
- Sergeant Major of the Army
- Sergeant Major of the Marine Corps
- Master Chief Petty Officer of the Navy
- Chief Master Sergeant of the Air Force
- Master Chief Petty Officer of the Coast Guard