Spain in the Axis turns Gibraltar into a battlefront

How would the Second World War change if Spain joined the Axis?

Gibraltar would become a major battle zone, and an Allied operation in Iberia could begin as a relief of Portugal before advancing through Spain toward France.

Spanish participation would be dangerous for Spain as well as troublesome for the Allies. The Strait of Gibraltar would see sustained fighting rather than occasional skirmishing. An Operation Torch-like landing could be framed as the relief of Portugal, followed by a modern version of the Peninsular campaign advancing through Spain and into France. Control of the western Mediterranean entrance would therefore become inseparable from an Iberian land war.