...Goins says this brand was first used by Koeller & Schmitz Cutlery Co of Solingen c1884. He adds that this company had sales offices in NYC and Dubuque, Iowa. [I suspect Koeller & Schmitz was in fact an American wholesale importer].
In April 1915, the British Royal Navy began a blockade of American ports, seizing German cargoes and citizens from neutral ships, including American ships.
American importers of German merchandise then scrambled to obtain or create domestic sources. Existing US knife factories were swamped with orders, so wholesalers who could afford to either bought factories, or set up new ones.
Fox began operating a factory in Milwaukee, Wis, at this time -- whether a new one, or the former Hatch Cutlery factory I do not know, but probably a new one.
The MADE IN USA - Fox knives on ebay date from this time, or possibly later, but not much later.
Goins says that Fox Cutlery Co. continued in business until c1955 --- BUT I suspect that after 1918, it was a wholesaler again, rather than a mfr. At that time (1955) the Fox brand was acquired by Schweizer Cutlery co., also of Wisconsin. He gives the dates 1922-1955 for Schweizer, so I suspect they acquired the Fox brand in 1922 -- but I don't know.
Anyway, the most likely date range for those knives is c1915-1922.
BRL...