With very few exceptions, becoming a non-commissioned officer (NCO) or petty officer in the U.S. Armed Forces 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.
Soldiers and armies have been prominent in popular culture since the beginnings of recorded history. In addition to the countless images of military leaders in heroic poses from antiquity, they have been an enduring source of inspiration in war literature. Not all of this has been entirely complementary, and the military have been lampooned or ridiculed as often as they have been idolised. The classical Greek writer Aristophanes, devoted an entire comedy, Lysistrata, to a strike organised by military wives, where they withhold sex from their husbands to prevent them from going to war.
Note: While the U.S. Navy is older than the Marine Corps, the Marine Corps takes precedence due to previous inconsistencies in the Navy's birth date. The Marine Corps has recognized its observed birth date on a more consistent basis. The Second Continental Congress is considered to have established the Navy on 13 October 1775 by authorizing the purchase of ships, but did not actually pass the "Rules for the Regulation of the Navy of the United Colonies" until 27 November 1775. The Marine Corps was established by act of said Congress on 10 November 1775. The Navy did not officially recognize 13 October 1775 as its birth date until 1972, when then–Chief of Naval Operations Admiral Elmo Zumwalt authorized it to be observed as such.
The first step that one will take after deciding to pursue a career in the military is taking the Armed Service Vocational Aptitude Battery test. This is more commonly referred to as the ASVAB. The ASVAB not only determines whether or not a candidate is qualified to serve in the armed forces but also shows which specific job they have the most aptitude for.
Development of military doctrine is perhaps the more important of all capability development activities, because it determines how military forces were, and are used in conflicts, the concepts and methods used by the command to employ appropriately military skilled, armed and equipped personnel in achievement of the tangible goals and objectives of the war, campaign, battle, engagement, action or a duel. The line between strategy and tactics is not easily blurred, although deciding which is being discussed had sometimes been a matter of personal judgement by some commentators, and military historians. The use of forces at the level of organisation between strategic and tactical is called operational mobility.
These forces demobilized in 1784 after the Treaty of Paris ended the War for Independence. The Congress of the Confederation created the current United States Army on 3 June 1784. The United States Congress created the current United States Navy on 27 March 1794 and the current United States Marine Corps on 11 July 1798. All three services trace their origins to their respective Continental predecessors. The 1787 adoption of the Constitution gave the Congress the power to "raise and support armies", to "provide and maintain a navy" and to "make rules for the government and regulation of the land and naval forces", as well as the power to declare war. The President is the U.S. Armed Forces' commander-in-chief.
Although some groups engaged in combat, such as militants or resistance movements, refer to themselves using military terminology, notably 'Army' or 'Front', none have had the structure of a national military to justify the reference, and usually have had to rely on support of outside national militaries. They also use these terms to conceal from the MI their true capabilities, and to impress potential ideological recruits.
Battlefield commission: under certain conditions, enlisted personnel who have skills that separate them from their peers can become officers by direct commissioning of a commander so authorized to grant them. This type of commission is rarely granted and is reserved only for the most exceptional enlisted personnel; it is done on an ad hoc basis, typically only in wartime. No direct battlefield commissions have been awarded since the Vietnam War. The Navy and Air Force do not employ this commissioning path.
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.
The development of breech loading had the greatest effect on naval warfare, for the first time since the Middle Ages, altering the way weapons are mounted on warships, and therefore naval tactics, now divorced from the reliance on sails with the invention of the internal combustion. A further advance in military naval technology was the design of the submarine, and its weapon, the torpedo.
In the 2000s, women can serve on U.S. combat ships, including in command roles. They are permitted to serve on submarines. 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.
One of the oldest military publications is The Art of War, by the Chinese philosopher Sun Tzu. Written in the 6th century BCE, the 13-chapter book is intended as military instruction, and not as military theory, but has had a huge influence on Asian military doctrine, and from the late 19th century, on European and United States military planning. It has even been used to formulate business tactics, and can even be applied in social and political areas.[where?]
As of 2017, the U.S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U.S. constitutes roughly 40 percent of the world's military expenditures. The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States. The U.S. Air Force is the world's largest air force, the U.S. Navy is the world's largest navy by tonnage, and the U.S. Navy and the U.S. Marine Corps combined are the world's second largest air arm. In terms of size, the U.S. Coast Guard is the world's 12th largest naval force. 
The meaning of military tactics has changed over time; from the deployment and manoeuvring of entire land armies on the fields of ancient battles, and galley fleets; to modern use of small unit ambushes, encirclements, bombardment attacks, frontal assaults, air assaults, hit-and-run tactics used mainly by guerrilla forces, and, in some cases, suicide attacks on land and at sea. Evolution of aerial warfare introduced its own air combat tactics. Often, military deception, in the form of military camouflage or misdirection using decoys, is used to confuse the enemy as a tactic.
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. Some armed forces allow a short discharge window, normally during training, when recruits may leave the armed force as of right. 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.