Regarding Army buttons on the belt in question, I don’t believe that the Eagle is necessarily, in this case, an Army insignia. It is a
a uniquely American version of the eagle, much like the US Presedential seal. Remember, this is a cataloged item from a commercial company. The Mills canvas .45 auto holster I had had an “Eagle button” fastener for the lid, and that is the holster they claim in the catalog is used with this belt. It is also the Mills Company’s own claim that it was Marine Corp Issue. They would have known who they sold this equipment to.
Rereading this (leading to this edit), another thing struck me. While the Mills catalog says the belt in question was adopted by the USMC, it does not say that it was exclusive to that service. In light of the Marine Corps M1911 Pistol magazine pouch shown later on this thread, with EGA Marine-specific buttons, it is possible that belts supplied to them had such buttons, but that the same equipment offered to other services, such as the Army, or various State National Guard or Militia troops, had other style of buttons. Just a thought.
Since the Mills catalog is a piece of primary-source documentation, I think we have to accept what they said, and not try to “outguess” the people who made the equipment. I know that in any commercial catalogs, there is a certain amount of hype, but trying to separate it from the truth, when any hype that might be there is in the primary-source documentation, strikes me as futil in the absence of documentation to the contrary. Further, at the time, the USMC was, I believe, a fairly small service, their primary mission being as shipboard troops. being trained and use to the rigors of life aboard ship, they were occasionally used for foreign incursions, as at Tripoli, but I don’t think it was until the American involvement in combat in WWI that the Marines were used as standard infantry, and it is before the time of the huge “landing craft” landings of the island fighting of WWII.