U.S.built Iranian aircraft

Chinooks in operation with Iran, some of them have been modified with flotation devices which are able to land on water

Very adventurous!

That modification if fairly standard for the Chinook. I know the brits have done that as have the US.
The Iranians Worked hard with the Russians to develup a lot of reverse enginering and life extention programs. They may look like there retiring American breathren but under the skin very little is the same.