Only if it's select fire. A "Main Battle Rifle" it ABSOLUTELY is. And among the finest of its breed, with a long and honorable record. An "Assault Rifle", not so much. Leastwise, not the way I ever understood the definition of "Assault Rifle", which specifies select fire, where the M1 is a semi-auto only rifle, and "generally uses smaller calibre ammunition than a main battle rifle". No slur on the .30 cal intended. It's a fine round, and you'll never hear me put it down. But it's a skosh large to fit the definition of "Assault Rifle" I'm familiar with.
Assault weapons also have the pistol grip and that shoulder thing that goes up to help maximize killing speed and power, doncha know...
Won't SOMEONE think of the chillllldrenn!!!
Of course, "Assault RIfle" is not to be confused with "Assault Weapon" or "Assault Style Weapon", which anyone qualified to have an opinion on the subject understands is a crock of media-political-babble shit made up and hyped to help scare the sheeple* into compliance.
* For the record, I detest Rush Limbaugh, and I disagree with damn near everything else I've ever heard him say, but he DID coin a very accurate term, so I gotta give him credit for it.