I Wonder...
I wonder how they're going to include Nazis and World War II, along with the Merlinian mythology, into this. Given Hitler was notable for sending his Nazi armies to find mythological artifacts, maybe they were trying to find some Cybertronian artifact, and by how it looks in the trailer, maybe there were some Transformers during that tie.
Wouldn't be surprised by such an idea, based on how the previous films' prologues revealed the Transformers being on Earth in the distant past - the 19th century, Ancient Egypt, Apollo moon landings, the dinosaur age, now WW2 and Merlin times.