Suez Canal and Middle East, as well as Atlantic patrols. The Germans also appreciated the strategic importance of north-west Africa for bases and as a route for any future American involvement. Therefore, the plans included the occupation of the region by substantial German forces, to forestall any future Allied invasion attempt. The plan, Operation Felix, was in detailed form before the negotiations failed at Hendaye. By March 1941, military resources were being ear-marked for Barbarossa and the Soviet Union. Operation Felix-Heinrich was an amended form of Felix that would be invoked once certain objectives in Russia had been achieved. In the event, these conditions were not fulfilled and Franco still held back from entering the war. After the war, Field Marshal Wilhelm Keitel said: "Instead of attacking Russia, we should have strangled the British Empire by closing the Mediterranean. The first step in the operation would have been the conquest of Gibraltar. That was another great opportunity we missed." If that had succeeded, Hermann Göring proposed that Germany "offer Britain the right to resume peaceful traffic through the Mediterranean if she came to terms with Germany and joined us in a war against Russia". As the war progressed and the tide turned against the Axis, the Germans planned for the event of an Allied attack through Spain. There were three successive plans, progressively less aggressive as German capability waned: Operation Isabella This was planned in April 1941 as a reaction to a proposed British landing on the Iberian peninsula near Gibraltar. German troops would then advance into Spain to support Franco and expel the British wherever they landed. Operation Ilona or Gisella Ilona was a scaled down version of Isabella, subsequently renamed Gisella. Devised in May 1942, to be invoked whether or not Spain stayed neutral. Ten German divisions would advance to Barcelona and, if necessary, towards Salamanca to support the Spanish army in fighting another proposed Allied landing either from the Mediterranean or Atlantic coasts. Operation Nurnberg Devised in June 1943, Nurnberg was purely a defensive operation in the Pyrenees along both sides of the Spanish-French border in the event of Allied landings in the Iberian peninsula, which were to repel an Allied advance from Spain into France. Resupply of German submarines Sources differ and list 25–26 cases of German submarines serviced in Spanish ports documented, taking place between January 1940 and February 1944: 5 in 1940, 16 in