In a pre CGI production, there are a few clunky moments, most obviously when action is superimposed over a backdrop, as in the pic of Rommel (Werner Hinz), above. But by and large everything is done on the grand scale - see above pics - and extremely well. The French attack on Ouistreham - and this is a rare WWII film in how well it addresses all the different sides, both within the Allied coalition, and their German adversaries - includes a masterful long shot (see pic. below), that looks like it must've been filmed from a tethered ballon, or something similar.
We see something of the build-up, and the tensions of anticipation, prior to the landings finally going ahead, including stuff on the important role of the weather. And we also see partisans, Free-French troops, and both American and British special forces and paras, operating behind the lines in advance of the landings. Meanwhile the Germans are beset by chaos, caused by in part by the aforementioned sabotage, plus their own ineptitude, and some plain bad luck.
 I've tried to refrain from nit-picking over the facts of history. But I feel I ought to mention that although Steele did get caught on the church tower - an accident that probably saved his life - he wasn't actually deafened by the church bells.
 Todd was himself present at Pegasus Bridge, during the Overlord operations, as a Captain.
 Well, more specifically, when Brig. Gen. Cota (Robert Mitchum) and co. finally get off the Omaha beaches.