Overlord's first sequence, which sees the soldiers jumping from a burning plane, was done by rigging a plane on a gimbal, actually blowing up the front, tilting it as if it were actually falling through the air, and sending stuntmen tumbling through real fire.
The movie featured more practical effects rather than the standard cgi effects most movies use. This was done to get a better reaction from the actors involved in the scenes where something gruesome would happen.
The "clickers" used by the squad after landing in France were called Crickets. Only the 101st Airborne Division was equipped with Crickets, and only the paratroopers of the division received it a few days before June 6, 1944.
The movie does not include any use of the swastika. Where it might normally be found, such as on the lighter or the Reichsadler eagle in the credits, the wendehorn rune is used.
In an interview with Jimmy Fallon, Wyatt Russell said he had mono while filming and that he lost around 25 pounds.