If you are planning to visit Ypres as well then I can recommend the following for the Ypres area:
In the assumption that you will take the Chunnel:
First visit Veurne, in Belgium; a small city in original flemish style (very different from what you are going to see in Normandy) and more or less the only flemish city of the whole WW I frontline that survived world war 1. All the rest, including Ypres, has been reconstructed after the war.
From there you could do Diksmuide. Skip the famous Diksmuide tower, which is more devoted to flemish independence than to the war anyway, but do visit the "dodengang" , a piece of world war 1 trench that is being maintained as far as possible in the original state.
From Diksmuide you can follow a (small) road along the old frontline up to Ypres. Whatever you plan, do be on time at the Menen Gate in Ypres for the Last Post, performed by the local fire brigade every day by 20.00 pm. Be there by 19.30h at the latest or you may not see/ hear much, sometimes there is a real crowd. Don't show up at the gate with roaring engines by 20.00pm. That is NOT appreciated.
The actual event only takes a few minutes but I've seen many leave it overwhelmed by emotion.
