I’m not arguing for/against .45 &/or 9mm. I was trying to answer the question you asked about whether or not the Army had a bunch of Thompsons & M-3 Grease Guns stored somewhere. I think the M-3 Grease Guns were finally purged from the Army inventory, mainly in armor units, during the last 20 years.
You’d be surprised what the army has stored. There are currently pre WW2 1911s (not A1s) going to be sold by the army CMP to the general public. Nothing gets tossed. Sold perhaps, shipped to allies, but not trashed.