In the U.S. Army, private refers to the two lowest enlisted ranks, just below Private First Class. The lowest rank (officially known as Private E-1 and sometimes referred to as recruit) wears no uniform insignia, while the second (Private E-2) wears the insignia shown here. Advancement to the higher version of private (with insignia) is currently automatic after six months time in service, but may get shortened to four months if given a waiver (but an automatic pay raise takes effect after four months of service, even absent advancement to Private E-2, meaning that the rank of Private E-1 has two separate pay grades).
In the U.S. Marine Corps, private refers to the lowest Marine Corps enlisted rank, just below Private First Class. A Marine Corps private wears no uniform insignia.

In the U.S. Army, Private First Class is the third lowest enlisted rank, just above Private and below Corporal or Specialist. It is equivalent to NATO Rank Grade OR-3. Originally no insignia identified holders of this rank, but in 1920 one chevron was established for it; then an arc was placed below the chevron in 1968 at the same time one chevron was authorized for the lower rank of private, in order to distinguish the latter from the still lower rank of recruit.

In the U.S. Marine Corps, Private First Class is the second lowest enlisted rank, just above Private and below Lance Corporal, equivalent to NATO Rank Grade OR-2.

Lance Corporal (LCpl or L/Cpl) is a military rank used by some elements of the British, Commonwealth, and U.S. armed forces. It ranks above privates and below corporal, although its specific status beyond that differs between the forces that use it. It is equivalent to the NATO Rank Grade OR-3. The origin of the rank of Lance Corporal derives from an amalgamation of corporal with the now-archaic lancepesade, formerly an NCO of the lowest rank. This in turn derives from the Italian lanzia spezzata, which literally means "broken lance" or "broken spear", but which was used to denote a seasoned soldier (the broken spear being a metaphor for combat experience, where such an occurrence was likely).
In the U.S. Marine Corps, Lance Corporal is the third lowest enlisted rank, just above Private First Class and below Corporal. It is not a non-commissioned officer military rank

In the U.S. Army a Corporal is the fourth enlisted rank, the first three being forms of Private. A Corporal ranks above a Private First Class and below a Sergeant, and has the same pay grade as a Specialist.
Unlike a Specialist, a Corporal is a non-commissioned officer and may direct the activities of other soldiers, including Specialists. Corporal is the most junior non-commissioned officer rank. A promotion from Specialist to Corporal is a lateral promotion; an increase in rank but not in pay grade.
It is common for a Corporal to lead a fireteam; however, if a soldier is promoted to Corporal and there are too many soldiers of that rank, the new Corporal will stay in his current position.

In the United States Army, although there are several ranks of sergeant, the lowest carries the title of Sergeant, referred to as buck sergeant when needed to distinguish it from the higher ranks. Sergeant is the fifth enlisted rank in the U.S. Army, just above Corporal and below Staff Sergeant, and is the second-lowest grade of non-commissioned officer.
Similarly, the United States Marine Corps has several ranks which carry the title of sergeant, the lowest of which is Sergeant. U.S.M.C. Sergeants are the fifth enlisted rank in the U.S. Marine Corps, just above Corporal and below Staff Sergeant.

Staff Sergeant (SSG) is the sixth enlisted rank in the U.S. Army, just above Sergeant and below Sergeant First Class, and is a non-commissioned officer. They are generally placed in charge of squads, but can also act as platoon sergeants in the absence of a Sergeant First Class.
Staff Sergeant is also the sixth enlisted rank in the U.S. Marine Corps, just above Sergeant and below Gunnery Sergeant, and is a staff non-commissioned officer

Gunnery Sergeant is the seventh enlisted rank in the U.S. Marine Corps, just above Staff Sergeant and below Master Sergeant and First Sergeant, and is a staff non-commissioned officer. They are assigned a pay grade of E-7 and the title may be abbreviated as GySgt.

Gunnery Sergeants are commonly referred to by the nickname "Gunny". This nickname is usually regarded as a title of esteem, and is generally acceptable for use in all situations except formal and ceremonial ones. Use of the term by lower-ranking personnel, however, remains at the Gunnery Sergeant's discretion.

A Master Sergeant is the eighth enlisted rank in the United States Marine Corps, just above Gunnery Sergeant, below Master Gunnery Sergeant, Sergeant Major, and Sergeant Major of the Marine Corps.

It is equal in grade to First Sergeant. It is abbreviated as "MSgt." Master Sergeants in the U.S. Marine Corps provide technical leadership as occupational specialists at the E-8 level. General command leadership at this paygrade is provided by the separate rank of First Sergeant.

In the United States Marine Corps, First Sergeant is one level below Sergeant Major and Master Gunnery Sergeant and is the next rank above Gunnery Sergeant. It is equal in grade to Master Sergeant, although the two ranks have different responsibilities. Unlike the first sergeant and master sergeant programs in the U.S. Army, no lateral movement is possible between the two ranks in the Marine Corps. In their annual performance evaluations, called "proficiency reports," eligible Gunnery Sergeants indicate whether they wish to be considered for promotion to Master Sergeant or First Sergeant, and thus whether they enter the promotional track for Master Gunnery Sergeant or Sergeant Major.

Master Gunnery Sergeant is the ninth and highest enlisted rank (along with the grade-equivalent ranks of Sergeant Major and Sergeant Major of the Marine Corps) in the U.S. Marine Corps. Master Gunnery Sergeants are staff non-commissioned officers (SNCOs), and are assigned a pay grade of E-9. The title may be abbreviated as MGySgt.
Master Gunnery Sergeants are sometimes referred to by the nickname "Master Guns" or "Master Gunny." These nicknames are unacceptable in formal or ceremonial situations, and, at the rank holder's discretion, may also be unacceptable for use by lower-ranking Marines.

In the U.S. Army, Sergeant Major refers to both a military rank and to a specific administrative position. The rank refers to the highest enlisted rank, just above First Sergeant, with a pay grade of E-9.
The administrative position, Command Sergeant Major, is the senior enlisted advisor to the commanding officer and carries with it certain ceremonial functions such as caring for the unit's colors.
Additionally, they serve as monitors for and advocates of the enlisted men in the command. This position exists in units of battalion size or larger.