Doesn’t the US Army have a heraldry unit that is responsible for for the lineage of units and their identifiers? I’d consider contacting them with this chestnut.
I’d start with what US units were authorized to wear berets, or may have worn them as part of a cover, during WWII. Then look for what flashes were authorized or allowed to be worn on them.
Since this is an English-made beret with a flash that alludes to General Washington’s coat of arms, part of me wonders if the item is a beret allowed for wear by Major William O. Darby’s early Rangers-in-training at their base in Carrickfergus (sic?), Ireland.
Since it’s proving elusive to internet-powered casual research, I wonder if there is an outside chance that this was a beret worn by an American volunteer (or volunteer unit) during the Spanish Civil War. I know there was a Lincoln Brigade. Wikipedia says there was an American George Washington unit among the International Brigades during the Spanish Civil War.
...Or maybe it is something that was very casual and unauthorized. Something American servicemen may have worn as part of their civilian clothing while on R&R in Western Europe that helped them to be a little less conspicuous.
Total WAGs here on my part on all this, but I hope to jog memories or open an alternate path to search. It’s a fun mystery!
Wow, thank you so much, I definitely will try your suggestions and report back.