Here is an interesting glimpse at the history of the Colt CAR-15.
https://www.americanrifleman.org/articles/2019/1/24/behind-enemy-lines-with-the-car-15-rifle/
The Colt AR-15 Resource
"A site dedicated to the history of the Colt AR-15 rifles, carbines and associated items"
The Colt AR-15 Resource 