Flags serve many purposes. They symbolize a people and represent national pride. Flags convey a shared history. Over the centuries, military units have carried flags and colors to affirm group identity. They build pride and morale and represent the group's honor. In battle, flags served as a rallying point when a formation was broken. Troops gathered around the flag to regroup, attack, or retreat. Flags marked specific individuals, locations, and functions such as hospitals and ambulances.

Infantry regiments regularly held trooping ceremonies. Colors were paraded up and down the line of assembled soldiers to music to make sure the men remembered the colors. A guard of non-commissioned officers usually protected flags and colors. Held in great reverence, a regiment's honor was embodied in its colors. The entire regiment was humiliated if its colors were lost in battle.

Bedford Flag This flag was present at the battle of Concord on April 19, 1775. It was carried by Nathaniel Page, a Bedford Minuteman. The Latin inscription "Vince Aut Morire" means "Conquer or Die." The arm emerging from the clouds represents the arm of God. The original can be seen at the Bedford Town Library.
Bennington or "Vermont" This flag flew over the military stores in Bennington, Vermont, on August 16, 1777. The American militia, led by General John Stark, defeated a large British raiding force, thus protecting the military supplies at Bennington. Note that this flag begins with a white stripe.
Betsy Ross This flag was adopted June 14, 1777 (Flag Day). The Continental Congress resolved on this day: "That the flag of the United States be thirteen stripes alternating red and white; that the Union be thirteen stars, white in a blue field, representing a new constellation." It is unknown who actually designed this flag. There is a slight possibility that John Paul Jones did. The Congress did not specify an arrangement for the stars in the canton; as a result, there are many variations in the flags that followed until 1912.
British Red Ensign or "Colonial Red Ensign" This is the best known of the British Maritime flags, or Ensigns, which were formed by placing the Union flag in the canton of another flag having a field of white, blue, or red. This flag is also known as the Meteor flag and was widely used on ships during the Colonial period. This was the first National flag of the United States.
Bunker Hill On the night of June 16-17, 1775, the Americans fortified Breed's and Bunker Hills overlooking Boston Harbor. Although they had not officially declared their independence, a fight was underway. When the British advanced up the slope the next day, they saw an early New England flag, possibly a red or blue banner. Many early Colonial flags had been made by altering the English flag, and most still contained a reference to the mother country. This demonstrated that the Colonists still saw themselves as British subjects but were declaring their right to be free from violation of their liberties.
Cowpens or "Third Maryland Regiment" The Cowpens was first carried by the Third Maryland Regiment, which was part of the Continental line of Maryland, Virginia, and Georgia regiments. On January 17th, 1781, General Daniel Morgan won a decisive victory against the British at Cowpens, South Carolina. The original flag is enshrined in the State House in Annapolis, Maryland.
Culpeper This flag represented a group of about one hundred minutemen from Culpeper, Virginia. The group formed part of Colonel Patrick Henry's First Virginia Regiment of 1775. In October-November 1775 three hundred such minutemen, led by Colonel Stevens, assembled at Culpeper Court House and marched for Williamsburg. As they marched through the country, their unusual dress alarmed the people. The words "LIBERTY OR DEATH" were in large white letters on the breast of their hunting shirts. They had bucks' tails in their hats and in their belts, tomahawks, and scalping knives.
First Continental Regiment or "First Pennsylvania Rifle Regiment" During the course of the Revolution, this regiment served in each of the thirteen colonies, and its banner was carried at the battles of Trenton, Princeton, Brandywine, Monmouth, and Yorktown.
First Navy Jack or "Continental Navy Jack" This flag is believed to have flown aboard the Continental Fleet's flagship Alfred, in January, 1776. This flag, or one of its variations, was used by American ships throughout the Revolution. ~ Background ~ The United States Navy originated as the Continental Navy, established early in the American Revolution by the Continental Congress by a resolution of 13 October 1775. There is a widespread belief that ships of the Continental Navy flew a jack consisting of alternating red and white stripes, having the image of a rattlesnake stretched out across it, with the motto "Don't Tread on Me." That belief, however, rests on no firm base of historical evidence. It is well-documented that the rattlesnake and the motto "Don't Tread on Me" were used together on several flags during the War of Independence. The only question is whether the Continental Navy actually used a red and white striped flag with a rattlesnake and the motto "Don't Tread on Me" as its jack. The evidence is inconclusive. There is reason to believe that the Continental Navy jack was simply a red and white striped flag with no other adornment. ~ Conclusion ~ The historical evidence makes it impossible to say for certain whether the Continental Navy used the striped rattlesnake flag as its jack. At the same time, the evidence does suggest strong connections between the symbol of the rattlesnake with the motto "Don't Tread on Me" and the United States' earliest naval traditions.
Fort Moultrie This flag was carried by Colonel William Moultrie's South Carolina Militia on Sullivan Island in Charleston Harbor on June 28, 1776. The British were defeated that day, which saved the south from British occupation for another two years. Some versions of this flag have the word "LIBERTY" in the crescent moon. The South Carolina state flag still contains the crescent moon from this Revolutionary flag.
Gadsden This flag was first used by Commodore Esek Hopkins, the first Commander in Chief of the New Continental Fleet. At the time that his ships initially put to sea in February, 1776, flags with the symbol of the rattlesnake were very popular in Rhode Island. Colonel Christopher Gadsden of South Carolina copied this flag and presented it to the Continental Congress. ~ Background ~ In early 1776 Commodore Esek Hopkins, the first and only commander in chief of the Continental Navy fleet, used a personal standard designed by Christopher Gadsden of South Carolina. This flag consisted of a yellow field with a coiled snake and the motto "Don't Tread on Me." There is no doubt as to the authenticity of Hopkins's personal standard, usually referred to as "the Gadsden flag. The only written description of the Continental Navy jack contemporary with the American Revolution appears in Commodore Hopkins' "Signals for the American Fleet," January 1776, where it is described as "the strip'd jack." No document says that the jack had a rattlesnake or motto on it. Elsewhere, Hopkins mentions using a "striped flag" as a signal. Since American merchant ships often displayed a simple red and white striped flag, there is a good chance that the striped jack to which Hopkins refers was the plain, striped flag used by American merchant ships.
Grand Union or "Continental Colors" This flag was never officially sanctioned by the Continental Congress but is considered the first flag of the United States and was in use from late 1775 until mid 1777. This flag was an alteration of the British Meteor flag. In its blue canton was the red cross of St. George, signifying England, and the white cross of St. Andrew, signifying Scotland. The thirteen stripes signified the original colonies. Retaining the British Union in the canton indicated a continued loyalty, as the Americans saw it, to the constitutional government against which they fought. On January 1, 1776, this flag was first raised on Prospect Hill (then called MT. Pisgah), in Somerville, Massachusetts. At this time the Continental army came into formal existence. At the time it was known as the continental colors because it represented the entire nation. In one of Washington's letters he referred to it as the "Great Union Flag," and it is most commonly called the Grand Union today.
Green Mountain Boys On August 16, 1777 the "Green Mountain Boys" fought under General Stark at the Battle of Bennington. Its green field represented their name, and the thirteen white stars were a tribute to the thirteen colonies. A notable victory of the Green Mountain Boys, under Ethan Allen, occurred on the morning of May 10, 1775, when they silently invaded the British held Fort Ticonderoga and demanded its surrender "In the name of the great Jehovah and the Continental Congress." The captured cannon and mortars were transported across the snow-covered mountains of New England, and their installation on the heights over Boston Harbor enabled Washington to force the British to leave that important seaport.
Guilford Courthouse This flag is an example of the lack of uniformity in American flags during the Revolutionary period as each group chose what flag to be used as its standard. This flag has the unique elements of an elongated canton and blue stripes. It was raised over the Guilford Courthouse in North Carolina on March 15, 1781 under the leadership of General Greene, whose militiamen halted the British advance through the Carolinas and turned them back to the seaport towns. This was one of the bloodiest battles of the long war, with the British losing over one quarter of their troops.
Philadelphia Light Horse Troop This troop was formed by a group of Philadelphia gentlemen on November 17, 1774. Many were businessmen and merchants who supplied their own uniforms, military equipment, and horses. The flag was contributed to the unit by Captain Markoe; it was designed by John Folwell and painted by James Claypoole. The British Union was originally painted in the canton, but the artist was instructed to paint thirteen stripes to represent the united colonies. It was this troop that escorted General Washington from Philadelphia to take command of the Continental Army, assembled at Cambridge, outside of Boston in June, 1775. The Light Horse Troop later carried its flag in the Battles of Brandywine, Germantown, Princeton, and Trenton.
Pine Tree This flag was in use 1775-1777. It was officially adopted by the Massachusetts Navy in April 1776. It flew over the floating batteries which sailed down the Charles River to attack British-held Boston. This flag is the jack form of the "Bunker Hill" flag. On October 20, 1775, Colonel Joseph Reed, Washington's military secretary, recommended that this flag be put into general usage so that American ships could recognize one another. The "Pine Tree Flag" is a generic name for a number of flags used by Massachusetts and by New England from 1686 to 1776.
Rhode Island Regiment In Rhode Island the anchor has been used as a state symbol ever since 1647, which is evident in the current State flag. The anchor represents Rhode Island's seafaring activities, and the thirteen stars symbolize the original thirteen colonies. The native Rhode Islanders were among the first to join the Minutemen outside Boston. The Rhode Island Regiments served at the Battles of Brandywine, Trenton, and Yorktown. This flag is preserved today in the State House in Providence, Rhode Island.
Sons of Liberty This was the flag of the early colonist who had joined together in the protest against the British impositions on American economic freedom. One such protest, occurring on October 7, 1765, was resistance to the Stamp Act. A delegate from each of the nine colonies formed the "Stamp Act Congress." They petitioned the king and parliament; the act was repealed on March 18, 1766. The flag of nine red and white stripes that represented these "Sons of Liberty" became known as the "Rebellious Stripes." On December 16, 1773, the Sons of Liberty protested parliament's Tea Act, an action that became known as the Boston Tea Party. The colonists believed the tax to be a violation of their legitimate economic liberty. Three and a half years after the Tea Party, the thirteen colonies had come together in their decision to fight for independence, and the nine stripes had grown to thirteen. The Sons of Liberty would rally under a large tree which became known as "The Liberty Tree."
Taunton This flag is another example of the colonists modifying the British flag, in this case the British Red Ensign. It was raised on the Liberty pole in Taunton, Massachusetts, on October 21, 1774. Sometimes only the word "LIBERTY" was added to the flag.
Washington Cruisers This flag was used by George Washington on his squadron of six schooners, which he outfitted at his own expense in the fall of 1775. This flag was a variation of the New England Pine Tree flag. It was later modified and adopted by the Massachusetts Navy. The Sons of Liberty would rally under a large tree, in Boston Massachusetts, which came to be known as "The Liberty Tree." This tree became a symbol of American independence. Knowing they were up against a great military power, they believed they were sustained by still a greater power, thus their "APPEAL TO HEAVEN." ~ Background ~ Col. Joseph Reed to Col. John Glover and Stephen Moylan, 20 October 1775, referring to Washington's fleet of schooners: "Please to fix upon some particular Colour for a Flag--& a Signal, by which our vessels may know one another-What do you think of a Flag with a White Ground, a Tree in the Middle-the Motto (Appeal to Heaven)-This is the Flag of our floating Batteries." Sir Hugh Palliser to Lord Sandwich, 6 January 1776, referring to the flag of the captured brig Washington, of George Washington's fleet: "Captain Medows has brought the American vessel's colours, it is a white field with a green pine tree in the middle: the motto, Appeal to Heaven." The Massachusetts General Court established the flag of the state navy on 26 July 1776: "that the Colours be a white Flagg, with a green Pine Tree, and an Inscription, 'Appeal to Heaven.'"

Sources:
American Flag and Gift website
Department of the Navy - Naval Historical Center