Not true. Japan decided not to attack the US on our home ground because they stated there would be a gun behind every blade of grass. They were right. Currently you have 1.3 million active duty military personnel.
Take out 25% for administration. Then you would have to deal with the ones who refuse to fire on American civilians. And then those who have families in the conflict.
Given the fact that this would only be in the case of hostile Government against its citizens I doubt you would have any US military to defend the government. Not enough to even begin to protect those in power.
You think military pilots are going to bomb American cities knowing they are killing their own families and families of other soldiers? No officer is going to order his soldiers against his sworn oath to defend the constitution. An armed conflict against this government would be ousting those who are violating the constitution.
Not to mention, In 2018, Small Arms Survey reported that there are over one billion small arms distributed globally, of which 857 million (about 85 percent) are in civilian hands. The Small Arms Survey stated that U.S. civilians alone account for 393 million (about 46 percent) of the worldwide total of civilian held firearms.
Best of luck with your idea that the US Military would obliterate an armed US militia. If I remember correctly, thats what the British thought as well, while an armed militia with muzzleloading squirrel guns,Bayonets, and tomahawks took out an entire opposing military force with cannons, ships, breech-loading rifles, the Pattern 1776 infantry rifle, and Brown Bess muskets that could fire 4 rounds per minute.