Final answer:
Chevrons became a permanent part of the NCO uniform in 1821 when the War Department revised the uniform regulations, establishing their size, color, and placement. Initially worn points down until 1902, the chevrons were then changed to be worn points up.
Step-by-step explanation:
In the history of the United States Army, chevrons were first approved for use on the uniforms of noncommissioned officers (NCOs) after the birth of the Army in 1775. However, it was not until 1821 that chevrons became a permanent part of the NCO uniform. This was when the War Department made a significant overhaul to the uniform regulations, specifying the size, color, and location of the chevrons. Initially, they were to be worn points down until 1902 when they were changed to be worn points up, a style that continues to signify NCO rank in the modern Army. The use of chevrons has generally denoted the rank and level of service of the wearer and are recognized as one of the oldest symbols of rank in the military worldwide.