Do Off world vehicles exist here on earth?

Of Course! They might not work any more sort of like crashed world war II vehicles from Russia, Germany, France, the U.S. Great Britain, Japan and other countries that have crashed under the ocean or on land somewhere but they exist. If you fly something from another planet here and it crashes it is a real thing and then governments tend to hide and to study how these things work.

Most of these craft are time space vehicles that travel time as well as space.

And since time travel (forward and backward through time) is the single most dangerous invention of all time, governments hide this information from the public (which is both good and bad) depending upon who actually has this information.

So, the mother craft (like battleships or aircraft Carriers) usually stay in space and just the little time space vehicles that are capable of 3000 to 7000 plus mile per hour speeds through the air are the ones that crash sometimes. The mother ships don't come to earth but stay in space just like Aircraft Carriers and battleships stay in the ocean but their helicopters and planes and trucks and small boats go everywhere.

Mother ships might also be under the ocean but never on land but can defend themselves from any technology of this era when they are in space or under our oceans.