We are going on the London / Paris tour in May. At the end of the tour we have extra days before we head home. We'd like to go to Bayeux to see the WWII sites, then go to Mont St Michel and then head back to CDG. Should we take the train or rent a car? Also if we took the train, does anyone know if there is a tour from Bayeux to Mont St Michel? Thanks very much!
You'll want a rental car. It's complicated to get to MSM by train and you can't get to the D-Day sites without a car.
What a great time of year to visit Normandy!
A car is not absolutely required but will help you make the best use of your time there and will extend your reach.
For instance, a car makes it easier to spend the night at Mt. St. Michel, which gives you the evening and morning without the crowds.
I'd take the train to Normandy and rent a car there.
We would also recommend a car. We rented in Versailles and drove to Arromanches, then along the beaches, cemetaries, on to Mont St. Michel, etc. We found driving in Normandy and Brittany the easiest in France, but also tried to avoid the big cities, especially at first.
There's very good information in the RS France book about all the WWII sites and info, as well as tour companies and where they depart from. Look at both the sections on Bayeaux, as well as the section on touring the D-Day beaches. The latter is where they list some of the tour companies.