Could anyone recommend a tour for a one day trip to see a few WWII sites? I certainly understand it is not sufficient time but it is the best we can manage this trip.
We found this to be a very doable day trip from Paris. Train to Caen and the museum there has guided van tours of the American beaches and cemetery. They will drop you back at the train station afterward (have to get to the museum on your own). Bring your passport, I was asked for it on the train.
An alternative that will give you more time at the invasion sites and less inside a museum is a tour offered by Overlord Tours for folks staying in Paris. You buy your own round-trip ticket from Paris to Bayeux, taking the early train. The tour van picks you up right at the Bayeux train station. You get essentially a full-day tour before being dropped off back at the Bayeux station. This means an early start, however.