We recognize December 13th as the birthday of the National Guard. On this date in 1636, the first militia regiments in North America were organized in Massachusetts. Based upon an order of the Massachusetts Bay Colony's General Court, the colony's militia was organized into three permanent regiments to better defend the colony. Today, the descendants of these first regiments - the 181st Infantry, the 182nd Infantry, the 101st Field Artillery, and the 101st Engineer Battalion of the Massachusetts Army National Guard – share the distinction of being the oldest units in the U.S. military. December 13, 1636, thus marks the beginning of the organized militia, and the birth of the National Guard's oldest organized units is symbolic of the founding of all the state, territory, and District of Columbia militias that collectively make up today's National Guard.

The official birth date of the Army National Guard as a reserve component of the Army is December 13, 1636. On this date, the Massachusetts colonial legislature directed that the colony’s existing militia companies be organized into three regiments. This date is recognized based upon the Department of Defense’s practice of adopting the dates of initial authorizing legislation for organized units as the birthdates of the active and reserve components of the armed services.

The oldest Army National Guard units are the 101st Engineer Battalion, the 101st Field Artillery Regiment, the 181st Infantry Regiment, and the 182nd Infantry Regiment, all of the Massachusetts Army National Guard. These four units are the descendents of the original three militia regiments organized by colonial Massachusetts legislation on December 13, 1636, and share the distinction of being the oldest units in the U.S. military.

Our ability to recognize December 13, 1636, as the organization date of the oldest Army National Guard units is based in law. The Militia Act of May 8, 1792, permitted militia units organized before the May 8, 1792, to retain their "customary privileges." This provision of the militia act was perpetuated by the Militia Act of 1903, the National Defense Act of 1916, and by subsequent law.

The official birth date of the Air National Guard as a reserve component of the Air Force is September 18, 1947. On this date, the first Secretary of the Air Force was sworn in to office per provisions of the National Security Act of 1947, the authorizing legislation for the United States Air Force and the Air National Guard. Soon afterwards, National Guard Army Air Forces units began to be transferred to the Air National Guard as a reserve component of the Air Force.

They’re not. The Air National Guard became the Reserve Component of the United States Air Force on September 18, 1947, when the Air Force broke from the U.S. Army to become a separate military service. Before 1947, the National Guard aviation units were part of the U.S. Army Air Forces. Some National Guard units trace their lineage before World War One. The original 29 National Guard aviation units were formally reorganized and activated beginning in 1921 to become part of the U.S. Army Air Corps and later the U.S. Army Air Forces which served in World War Two with great distinction. At the time when the Air Force was created in September, 1947 as a separate service, there were 59 aviation units in the National Guard, to include the original 29 observation squadrons which were mobilized in 1940. These units were all transferred from the Army Air Forces to the new Air Force effective April 27, 1948.

The oldest Air National Guard unit is the 102nd Rescue Squadron of the New York Air National Guard. This unit was originally organized in accordance with existing law, and authorized in the New York National Guard as the Aero Company, Signal Corps, on November 22, 1915. The oldest Air National Guard unit in continuous existence since its organization is the 109th Airlift Squadron of the Minnesota Air National Guard, which was organized and federally recognized as the 109th Observation Squadron, on January 17, 1921.