Hitler and his high command had planned for the eventual capture of Gibraltar. Had they been able to more successfully pressure Franco into cooperating .... and had the Axis been successful, then future Allied operations in the Med would have been seriously compromised.
Had such an operation been carried out and had Operation Barbarossa been delayed in doing so, who would have helped Britain defend Gibraltar (or invade Spain)? The Spanish Republic in exile? Certainly the Russians would stay out of it this time. After the U.S. entered the war and Operation Torch is carried out would be too late.
