In the U.S. Military services, rank determines who gets to tell whom what to do. The higher one's rank the more authority (and responsibility) they have. U.S. Military personnel fall into one of three categories: (1) enlisted members, (2) warrant officers, and (3) commissioned officers. Warrant officers outrank all enlisted members, and commissioned officers outrank all warrant officers and enlisted members.
"Rank" and "pay grade" are closely associated terms, but not quite the same. "Pay grade" is an administrative classification, associated with a member's pay. "Rank" is a title and denotes the member's level of authority and responsibility. An E-1 is the lowest enlisted pay grade. That person's "rank" is a "Private" in the Army and Marine Corps, an "Airman Basic" in the Air Force, and a "Seaman Recruit" in the Navy and Coast Guard. I should also probably note here that in the Navy and Coast Guard, the term "rank" is not used among enlisted Sailors. The proper term is "rate."
Through the ages, the badge of ranks have included such symbols as feathers, sashes, stripes and showy uniforms. Even carrying different weapons has signified rank. The badges of rank have been worn on hats, shoulders and around the waist and chest.
The American military adapted most of its rank insignia from the British. Before the Revolutionary War, Americans drilled with militia outfits based on the British tradition. Sailors followed the example of the most successful navy of the time -- the Royal Navy.
So, the Continental Army had privates, sergeants, lieutenants, captains, colonels, generals, and several now-obsolete ranks like coronet, subaltern and ensign. One thing the Army didn't have was enough money to buy uniforms.
T o solve this, Gen. George Washington wrote, "As the Continental Army has unfortunately no uniforms, and consequently many inconveniences must arise from not being able to distinguish the commissioned officers from the privates, it is desired that some badge of distinction be immediately provided; for instance that the field officers may have red or pink colored cockades in their hats, the captains yellow or buff, and the subalterns green."
Even during the war, rank insignia evolved. In 1780, regulations prescribed two stars for major generals and one star for brigadiers worn on shoulder boards, or epaulettes.
The use of most English ranks carried on even after the United States won the war. The Army and Marine Corps used comparable ranks, especially after 1840. The Navy took a different route.
The rank structure and insignia continued to evolve. Second lieutenants replaced the Army's coronets, ensigns and subalterns, but they had no distinctive insignia until Congress gave them "butterbars" in 1917. Colonels received the eagle in 1832. From 1836, majors and lieutenant colonels were denoted by oak leave; captains by double silver bars -- "railroad tracks"; and first lieutenants, single silver bars.
In the Navy, captain was the highest rank until Congress created flag officers in 1857 -- before then, designating someone an admiral in the republic had been deemed too royal for the United States. Until 1857, the Navy had three grades of captain roughly equivalent to the Army's brigadier general, colonel and lieutenant colonel. Adding to the confusion, all Navy ship commanders are called "captain" regardless of rank.
With the onset of the Civil War, the highest grade captains became commodores and rear admirals and wore one-star and two-star epaulettes, respectively. The lowest became commanders with oak leaves while captains in the middle remained equal to Army colonels and wore eagles.
At the same time, the Navy adopted a sleeve-stripe system that became so complex that when David Glasgow Farragut became the service's first full admiral in 1866, the stripes on his sleeves extended from cuff to elbow. The smaller sleeve stripes used today were introduced in 1869.
Chevrons are V-shaped stripes whose use in the military go back to at least the 12th century. It was a badge of honor and used in heraldry. The British and French used chevrons -- from the French word for "roof" -- to signify length of service.
Chevrons officially denoted rank in the U.S. military for the first time in 1817, when cadets at the U.S. Military Academy at West Point, N.Y., wore them on their sleeves. From West Point, chevrons spread to the Army and Marine Corps. The difference then was chevrons were worn points down until 1902, when Army and Marine Corps enlisted personnel switched to the present points up configuration.
Navy and Coast Guard petty officers trace their insignia heritage to the British. Petty officers were assistants to the officers aboard ship. The title wasn't a permanent rank and the men served at the captain's pleasure. Petty officers lost their rank when the crew was paid off at the end of a voyage.
In 1841, Navy petty officers received their first rank insignia -- an eagle perched on an anchor. Ratings -- job skills -- were incorporated into the insignia in 1866. In 1885, the Navy designated three classes of petty officers -- first, second and third. They added chevrons to designate the new ranks. The rank of chief petty officer was established in 1894.
During World War II, the Army adopted technician grades. Technicians of a given grade earned the same pay and wore the same insignia as equivalent noncommissioned officers except for a small "T" centered under the chevrons. Technicians, despite the stripes, had no command authority over troops. This evolved into the specialist ranks, pay grades E-4 to E-7. The last vestige today survives plainly as "specialist," pay grade E-4. When there were such people as specialists 7, they wore the current eagle symbol surmounted by three curved gold bars -- often called "bird umbrellas."
(Much of the above information courtesy of the American Forces Press Service )