Final answer:
The NCO support channel was formally recognized on December 20, 1976, when it was included in the U.S. Army's Field Manual 22-100.
Step-by-step explanation:
The NCO support channel was formally recognized on December 20, 1976. This was when the United States Army officially included the NCO support channel in its Field Manual 22-100, a manual that outlines leadership responsibilities and functions within the Army. The introduction of the NCO support channel was a significant development, as it structured the way non-commissioned officers provide support to their officers and conduct their duties.