420K was a lowball figure thrown out. Still too low. The ratio is something like 8 support troops for every one in the field. Don’t know much about the Army but in the AF on a typical base only about 1/4 of the populace is involved in aviation activities. This is on the bases with an aviation component.
Keep in mind that the number does not include contracted support staff that is expanded based on the mission. Also, the technology gains have made the Army more efficient, thus requiring fewer ground forces.
The comparisons to pre WWII numbers is not valid either. The 1940 number for the Army included the entire USAAF at the time.
I don’t see us getting into set piece tank battles outside of Kiev anytime in the next six months or so.