During the Civil War, the Confederacy used its national flag as a battle flag and later used two flags specific to the war: the Stainless Banner and the Blood-Stained Banner. Both sides of the Civil War carried battle flags that identified the fighting unit's country and regiment.
Early in the war, the Confederacy used its national flag as a battle flag: two red stripes and one white, with a blue box or canton containing seven stars. It later adopted specific battle flag designs to prevent confusion with the U.S. flag. The most famous Civil War battle flag features a blue and white star-spangled "X" on a red field. This was the regimental flag of General Robert E. Lee's unit, the Army of Northern Virginia, and was never used during the war as a national battle flag.
The blue and white "X" on a red field, while never used nationwide, was incorporated into the two national Confederate battle flags, but only as a part of their designs. The Stainless Banner had a canton featuring the Robert E. Lee design upon a pure white field, while the Blood-Stained Banner placed the canton upon a white field with a vertical red stripe on its far edge.
The Union also used several battle flag designs. All Union units carried both the standard United States flag of the time and a battle flag unique to each regiment. Some of these regimental flags were very similar to the national flag, differing only in how the stars on the blue canton were arranged; this was the case for the flag used at Fort Sumter. In other cases, the regimental battle flags were very distinct. For example, the flag used by the 28th Regiment of Massachusetts was green and incorporated symbols to reflect the unit's Irish heritage.