The trains are really good transportation. I flew into Paris and took the train to Normandy Beach. It doesnt go right to it, but it will get you real close.
I also went there by Eurostar train from London through the Chunnel.
Here is a good link.
https://www.thetrainline.com/en-us/via/europe/france/how-to-visit-normandys-d-day-beaches-by-train
Also took the train from London through the Chunnel. Went to Paris at speeds up to 236 km per hour. Amazing train and very smooth. Speed was so fast it made vehicles on the motorway next to the tracks look like they were going backwards.