ACU Patches, known broadly as shoulder sleeve insignia (SSI), are embroidered patches used by major formations of the United States Army. Each formation has a unique formation patch, and the U.S. Army is unique among the Armed Services in that all soldiers are required to wear the patch of their headquarters as part of their military uniforms.
Shoulder sleeve insignia are most commonly worn on the upper left shoulders of all U.S. Army uniforms, though they can be placed on other locations, such as a combat helmet. Shoulder sleeve insignia worn on the upper right shoulders on Army uniforms denote former wartime service. These "combat patches" will not be worn on the new Army service uniform. Instead a 2-inch metal replica will be worn on the right breast pocket and is officially known as the Combat Service Identification Badge.
The subdued version created for the Army Combat Uniform is the version widely used in the field today. Since the Army-wide adoption of the ACU, SSI for the ACU have been developed. These SSI are primarily foliage green, light brown, and black, though a few patches also feature red and maroon colors for some details. Unlike previous patches, the ACU SSI are velcro, designed to attach to the velcro pockets on the shoulder of the uniform, instead of being sewn on. This makes them easier to remove and replace.