A stellar piece of American military history. "Mule" in this case refers to messinger rather than the animal, though it is possible that these bags did actually ride on an Army mule at some point.
The leather is close to pristine! Still supple with no crazing or checking ... but if it were me I would put some conditioner on them as that would keep them working for another 100 years or so. But as is, these are a rare find indeed.
The description is from the 1916 Quartermasters manuel ... a reprint copy of which will come with these beauties.
These are roughly 8" x 12" as to the bags and pockets; another 6"-8" for the joinder leather and lacing. The Harbison and Gauthright maker's stamp is clear and deep. The USQMC is for the United States Quartermasters Corp. I've only seen one other set and they were in very bad shape ... and still danged pricey. This is a real treasure from the past.