Dinan a base for Mont St Michel,best base for Normandy?

I think you would like Bayeux.

I imagine you would have to take a taxi the 37 miles from Dinan to Mont St Michel. Mont St Michel hours are 9:30 am to 6 pm from September to April and 9 am to 7 pm from May to August.

Everything in Mont St Michel is uphill. There are no horizontal surfaces. You are always going uphill. Dinan also has some very steep streets. Dinan is lovely and I plan to return there. Because my tour group spent the night on Mont St Michel, I was able to get up at dawn and get some wonderful photographs from the part way up fortress.

In regards to Chartres, the ten year long restoration of the interior is reported to have been completed earlier this year so it will look better than it has in 500 years. It should be beautiful. There doesn't seem to be anything else of any age or significance nearby but the rest of the town is nice. The French-Vietnamese restaurant 'BB Soup' is great. It is downhill & to the right from the parking lot that is between the cathedral and the train station. Closed Mondays.

I guess you know that you can take the train from CDG to the Paris station and from there connect to Chartres. At the Paris train station, they don't announce the track a train is departing from until about 15 minutes before departure so just be patient.

You can also book a full day tour of Mont St. Michel and get so much additional history of not only the Mont.....but construction, surrounding areas etc.

Dinan is located in Brittany (Bretagne), not in Normandy. Mont St Michel is at the border between the two regions. Dinan is one of the good bases to visit the north coast of Brittany (St Malo, Cancale, Mont St Michel, Fougères, etc.). Bayeux or Caen would be good bases to visit WWII historic places (there are trains from Pontorson, near Mont St Michel).
You may find some information about transport (and tours) to reach / leave Mont St Michel on http://visite.bretagne.free.fr/index.php/en/nature/mont-saint-michel.html

I liked Dinan a lot and think it would be an attractive base. However, Bayeux is geographically probably the best option for visiting the D-Day sites. And it has been reported here (I have not verified) that the Hotel Churchill in Bayeux runs day-trips to Mont St-Michel. If you will be satisfied with a day-trip, it would be worth considering using Bayeux as a base for everything. It is my impression that the hotel's trips are open to people not staying in the hotel. I do not know whether they are full-fledged tours or are just transportation.

Caen is another good base for Normandie. It really depends on what you want to see. I start with the sights, then pick something that's central to those sights. Bayeux is about an hour an a half drive to MSM and close to Caen. Honfleur is also a popular stop.

So many options. You have provided a variety of possibilities for our 12 days in the area. logistically, we wish to avoid renting a car. That will be our greatest challenge. The experience will be moving, enlightening and culturally enriching, thanks to all.

It is a challenge to visit the D-day sites without a car. I suggest you get a book with extensive coverage of the Bayeux area (like our host's, Rick Steves, but there are others) to figure out which museums and outdoor places are "musts" for your own particular interests. Hiring a local guide is an expensive but convenient option. American demand for highly planned and guided tours of the D-Day beach areas are in high demand, and priced accordingly. But it does provide its own transportation.

No one has posted recently here about the MSM shuttle bus from one hotel in Bayeux, The Churchill. We had a car, so this is not a "recommendation". But others have found it useful in the past-especially for those with limited time and with the beaches as a priority. Maybe use the search box here if it interests you.

I agree with other posters about staying in Bayeux for the D-Day beaches and signing up for a day-long tour. There are some guides that use minivans and take small groups--I'd look at those options rather than a big bus. There are also two options for taking a bus from Bayeux to Mont St-Michel, so you wouldn't even have to stay in Dinan at all. However, these buses arrive at the island with all the other tourist buses--and the place is jammed during the day. Have you considered taking the train and bus to Mont St-Michel and staying on the island overnight? It is magical once the crowds leave. SNCF (the French rail system) has two options--take a TGV from Paris to Rennes, where you meet their bus that takes to directly to MSM, or take a regional train to Portorson, the closed train station to MSM, where a bus will take to you to island. For both options, it's all on one ticket and the transfer is easy.