Final answer:
NCOES became mandatory for promotion in the U.S. Army in 1980, setting the standard for the professional military education required for non-commissioned officers before advancing in rank.
Step-by-step explanation:
The Non-commissioned Officer Education System (NCOES) became mandatory for promotion in the United States Army in 1980. Prior to this change, professional military education was encouraged but not strictly required for promotion to most ranks. The implementation of the NCOES ensured that every non-commissioned officer (NCO) received the necessary training and education to perform at a higher level prior to promotion. This system has evolved over the years and is now known as the Non-commissioned Officer Professional Development System (NCOPDS), which continues to emphasize the importance of education and training in the professional advancement of NCOs.