Deciphering Enlistment Record from NARA AAD

The only record available from NARA for my father was a microfilm record of his enlistment. Most is pretty self explanatory but the one that I have questions about is "Source of Army Personnel" which says "National Guard". Does this mean that my father initially joined the National Guard and sometime after that was transferred to Regular Army?

I have attached a file with details. View attachment 21958

 

Army Serial Numbers beginning with 20 were assigned to National Guardsmen who were federalized. So he would have enlisted with the NG on 17 Jan 1941, according to the enlistment record you provided.

 

TD-Tommy776: thank you!