Here’s my proposed setup for Nationalist, Republican, and Basque Navies based on historical navies at the beginning of the war (with some alterations for balance). Unfortunately, the map doesn’t really allow for interesting naval situations. I’m considering adding a backdrop for the map that expands the ocean with more seazones.
Cape Ortegal: 1 Destroyer, 1 Cruiser, 1 Battleship
Cape Finesterre: 2 Cruisers
Bay of Biscay: 1 Battleship
Alboran Sea: 1 Destroyer
Cape of Palos: 3 Submarines, 4 Destroyers
Gulf of Cadiz: 1 Cruiser
Bay of Setubal: 1 Destroyers, 1 Cruisers
Republican Allies Navy
Bay of Biscay: 2 Destroyers
Even though they didn’t send ships until 1937, you could add Italian (Nationalist Allies) ships to the Mediterranean.
Nationalist Allies Navy
Gulf of Leon: 2 Submarines, 4 Destroyers, 1 Cruiser