There are quite a few novels where modern nations or villages or warships get transported back in time. Not so much across dimensions though.

Thus, it is the time when the ring quest is about to start. Still in the planning stages. England in the 1860's appears off the shores of Middle Earth. They come up to speed and join the Council - how does this change things? They get all the ships in port.

Didn't want to use a modern nuclear UK as seeing whether the ring could take an H-bomb isn't that interesting. If dragon fire was postulated as possibly melting it - don't want a techy solution.

Note, there was a Charles Stross novel where elves fleeing from a Lovecraftian invasion, port to modern UK. All kinds of magic weapons, dragons, etc. but they get their butts kicked and enlisted in the UK armed forces. However, the UK becomes ruled by a Lovecraft god and the book series fell apart for me. The USA becomes a vassal of Cthulhu. I don't know if Stross has figured out how to safe that Earth.

Then there is also the Gate anime.