US Military Flags
The use of military flags goes back hundreds of years, but it was probably in the Middle Ages that it became popular for warriors to carry flags with them into battle. When soldiers were all dressed up in their suits of armor it was difficult to tell who was who, so the introduction of military flags in battle was basically to let you know who your friends and enemies were.
As time progressed most of the world's armies, navies, and air forces etc. had their own individual flags designed for them. There are flags that represent each branch of the military, the navy or army etc. as a whole. Then there are flags that represent different brigades, divisions, squadrons, regiments, battalions and officers etc. within each of those branches. There are literally dozens of military flags including ones for the military police, army bands, the military chapel, the chief of engineers and the surgeon general etc.
The US has flags for the army, marine corps, navy, air force, and the coast guard; with the army, navy and marine flags being first created in 1775. These flags have been flown and used in every battle the US has fought, even during the country's own civil war.
Another US military flag that is quite popular is the POW/MIA flag which symbolizes American prisoners of war and all those who have gone missing in action. The flag was created in 1971, by a former World War II pilot, and although it grew from the Vietnam War it has come to represent all of those missing in action, back to World War II; a group of almost 90,000 people.
The US also has a military flag which represents all of its armed forces. There is also a Service Star flag which is flown by the families of people serving in the forces during times of war.