Mike Plaiss here - I think we have exchanged some info before.Been a while since I've been active so I am just now seeing this.We likely have the same info on John.According to the family history we received from Griffin Pleiss (grandson of Christian Phillip Pleiss, great-grandson of John Plaiss) John served five years in the French army as a drummer boy, and went in at the age of 14. I have no idea how Griffin knew this but his grandfather lived well into his eighty's so it likely came from him.
All that said I have spent some time thinking about it and here's what I came up with. First of all if he went in at the age of 14 then he went in sometime in 1808 or late '07. If he served five years then he was out no later than 1813.Waterloo was fought in 1815, so all of those facts can't be true.My guess (and it's just a guess) is that the age and the length of service are likely true and he wasn't at Waterloo.Being at Waterloo seems to be the most likely thing that got added to the story later.
Was he in the French army at all?That seems likely.His region of Wuerttemberg was quickly taken over by Napoleon and the local dukes were expected to provide men and equipment for Napoleon's army (so I've never known where to look for his military records - France or Wuerttemberg).
But anyway it is my theory that this is where the whole Pl-AI-ss spelling came from in the first place.(John and some of his children are the only ones to have used it - none of his brothers did). Genealogists I have talked to tell me that military service is often how names get changed. There is an incentive to continue to use the misspelled name - to collect your military pension.Furthermore, if a Frenchman were to misspell Pleiss it is reasonable to think that they would do it Plaiss.Most people assume my name is French, not German.
I know there is nothing definitive there, but I hope that helps. And if you have any thoughts on were we can find his military records, please share them.