John,
A very quick and admittedly incomplete response:

“..... and when true blue well experienced Aussies soldiers, often still serving or retired in recent years actually comment, they think the civlian armed force against a modern military force is a bit of a joke. .....”

- The Taliban with AK-47’s and IED’s have kept the pressure on modern “Coalition” and the ANA . Iraq was much the same.

What one would have to keep in mind, at least as far as the USA is concerned, is that there would be no guarantee that the full complement of the US Armed Forces would engage in warfare against US Citizens if ordered to do so.
The Oath of Office for all US military officers “swears or affirms” to uphold the “Constitution of the United States”, this is plainly distinct from required allegiance to an anti-Constitutional government administration that would go to war against its citizen populace.

There plausibly could be the occasion where parts of the US military or States National Guard actually oppose the government ordered use of force against the civilian population. ie: civil war.
.......Add to that the sheer numbers of civilians with prior military training.

- Mike