A lot of people ask, “Why is the US flag reversed when it’s on an arm patch of a US military?”
The place of honor for the American flag is always to the right of other organizational flags like the USMC or Navy flags. When carried with an organization flag as in the March of the Colors, the U.S. flag is carried to the right of the line of march.
Basically, the idea behind the backward American flag on Army uniforms is to make it look as though the flag is flying in the breeze as the person wearing it moves forward.
A normal flag would symbolize retreat as it stands still, but the flag shifts direction in the wind as the flag bearer advances. This symbolism was updated to reflect troops advancing in battle and was updated in 2003 for army regulations.
During the Civil War, both mounted cavalry and infantry units would designate a standard bearer, who carried the flag into battle. As this standard bearer charged, his forward momentum caused the flag to stream back.
Since the Stars and Stripes are mounted with the canton closest to the pole, that section of the flag stayed to the right, while the stripes flew to the left. Therefore, the flag is worn on the right shoulder, and wearing it backward gives the effect of the flag flying in the breeze as the wearer moves forward.
In 2003 the uniform regulation for the Army was updated. Army Regulation 670-1, “Wear and Appearance of Army Uniforms and Insignia,” addresses explicitly the proper and lawful placement of the U.S. flag patch on the Army uniform.
The regulation states that the stars are to face forward. When authorized for application to the proper uniform the American flag patch is to be worn, right or left shoulder. One of the flags will, therefore, be reversed (right shoulder) in order to adhere to the regulation and custom of having the stars facing forward. The term, “Assaulting Forward” has been adopted by combat troops (instead of “facing forward”).
The appropriate flag (color or subdued) for the right shoulder sleeve is identified as the reverse side flag.