Help Wanted U-Boot sunglasses?

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Can anyone help me out with this one
I bought this sunglasses many years ago and the seller told me they where U-BOOT Sunglasses !

but on the internet i coudn't find any prove iff that';s correct
It is made from alluminium and the glasses are interchangeable and tinted.

If it's not a U-Boot sunglasses what is it then Kriegsmarine or heer ?

Please help me out !

BY the way there are no markings on it

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U-Boot sunglasses

And another picture

[me6_130]

It is no german military model I know, sorry.

Carles