'Felix' (i) was a German unrealised plan to take Gibraltar and close the Strait of Gibraltar to British shipping and, in the event that Spain co-operated, seize the Canary, Cape Verde and Azores island groups (14 August 1940/9 May 1941).

Adolf Hitler was unaware that his own envoy, Vizeadmiral Wilhelm Canaris, the head of the Abwehr (intelligence service), was running a secret resistance movement and was liaising closely with General Francisco Franco y Bahamonde, the Spanish dictator, by specifying particular terms that Hitler was certain to refuse, and thereby ensuring that the negotiations would fail.

After the German defeat of France in June 1940, Reichsmarschall Hermann Göring, commander-in-chief of the Luftwaffe, advised Hitler to occupy Spain and North Africa, rather than implementing the 'Seelöwe' plan to invade and conquer the British isles. As early as June 1940, before the armistice with France had been signed, General Heinz Guderian also argued for the seizure of the UK’s strategically-important naval base of Gibraltar, which controlled access into the Mediterranean from the west. Guderian even urged Hitler to postpone the armistice so that the German forces could rush on through Spain with two Panzer divisions, take Gibraltar and invade French North Africa. General Alfred Jodl, the Oberkommando der Wehrmacht’s chief of operations, presented Hitler with a formal plan to cut the UK from the eastern parts of its empire by invading Spain, taking Gibraltar, invading North Africa and and finally advancing to the Suez Canal, instead of invading the UK.

On 12 July 1940, the Oberkommando der Wehrmacht established a special group for the necessary planning. On 22 July, Canaris, who was an acknowledged expert on Spanish affairs, travelled with several other German officers to Madrid for talks with Franco and the Spanish war minister, General Juan Vigón. They then travelled on to Algeciras, where they stayed some days to reconnoitre the approaches to Gibraltar, and then returned to Germany with the conclusion that Franco’s regime was reluctant to enter the war. However, Canaris was later found to have secretly run a resistance movement, and it is suspected that he actively discouraged Franco from joining the Axis. However, Canaris’s group did determine that Gibraltar might be seized by an air-supported ground assault by at least two infantry regiments, three engineer battalions and 12 artillery regiments. Canaris declared that without 380-mm (15-in) super-heavy assault artillery, which he knew was unavailable, Gibraltar could not be taken. When he reported to Generalfeldmarschall Wilhelm Keitel, the chief of the Oberkommando der Wehrmacht, Canaris gave his opinion that even if Germany could, with the co-operation of Spain, seize Gibraltar, the British would land in Morocco and French North-West Africa and West Africa.

In August, Canaris met with Franco’s brother-in-law, Ramón Serrano Súñer, who was about to become the Spanish foreign minister. Canaris urged Serrano Súñer to do what he could to convince Franco to stay out of the war. Soon after this, Franco sent Serrano Súñer to Berlin to get an idea of Hitler’s attitude since Canaris had assured him that Germany would not forcibly intervene in Spain. When Serrano Súñer met Hitler on 16 September, the German leader did not press very hard for Spanish involvement in the war, perhaps because he himself planned to meet Franco himself in the near future.

Canaris met with Franco around the same time and warned him that if Spain joined the Axis, the Spanish islands and even the Spanish mainland would be at risk from British amphibious and naval attack. Knowing that Franco feared a German invasion of Spain if he refused to co-operate, Canaris informed the Spanish leader that Hitler had no such intention because of the planned 'Barbarossa' invasion of the USSR. Canaris also surprised Franco by admitting that he was convinced that Germany could not win the war.

Confident because of his secret talks with Canaris, on 8 August Franco presented to Eberhard von Stohrer, the German ambassador to Spain, with extravagant terms for his co-operation. Stating his terms for joining Hitler, Franco demanded that Spain must be promised Gibraltar and French Morocco, and that Germany must also promise military and economic assistance in the form of wheat and oil to help Spain’s faltering economy. Additionally, German forces must first land on the British mainland in a full-scale invasion.

These demands provoked Hitler into sending Canaris to Spain once more in an effort to convince Franco to join the Axis and to scale back his 'outrageous' demands. In fact Canaris once more reminded Franco that it would be foolish to join the side that was doomed to lose the war.

On 24 August, Hitler approved a general plan to seize Gibraltar, and on 23 October met Franco at Hendaye in south-western France and proposed that Spain enter the war on the Axis side as early as January 1941. Gibraltar would be taken by German special units and turned over to Spain, but Franco refused the offer and emphasised Spain’s need for large-scale military and economic assistance. Hitler took offence when Franco expressed doubts about the possibility of a German victory in fighting the British on the latter’s home territory. Franco also pointed out that even if the British isles were invaded and taken, the British government, as well as most of the British army and the powerful Royal Navy, would probably retreat to Canada and continue the Battle of the Atlantic with the support of the USA.

A meaningless memorandum of understanding was signed at Hendaye by Franco and Hitler, with neither getting what he wanted. A few days later, Hitler was reported to have told Benito Mussolini, the Italian dictator, 'I would rather have four of my own teeth pulled out than go through another meeting with that man again!'

Despite those problems, the German military leadership was proceeding with work on 'Felix' (i) as a large-scale operation against Gibraltar. The German plan called for two corps to enter Spain across the western end of Pyrenees mountains from the German-occupied zone of south-western France to reach Irun in the Basque region, and then to advance via Burgos and Madrid, with westward spurs to Valladolid and Cáceres, before finally attacking the British fortress from the landward side with the aid of super-heavy tracked artillery. The XLIX Gebirgskorps, under the command of General Ludwig Kübler, was to cross Spain and assault Gibraltar, and the other, an expeditionary force based on General Rudolf Schmidt’s XXXIX Corps (mot.), was to secure its flanks and rear. Air support would need one fighter and two dive-bomber wings. Overall command of 'Felix' (i) was to be assigned to Generalfeldmarschall Walther von Reichenau, commander of the 6^th Army in France. Air support was to be provided by General Wolfram Freiherr von Richthofen’s VIII Fliegerkorps with eight dive-bomber Gruppen, two fighter Gruppen and five reconnaissance Staffeln.

The plan also made provision for the occupation Spanish possessions in North-West Africa (Spanish Morocco and Río de Oro) as well as the Canary and Cape Verde island groups, whose ports could then be used as bases for U-boats to operate more deeply and more lengthily into the central and southern Atlantic. In overall terms. therefore, the German plan was posited on the thinking that the loss of Gibraltar would deny the British navy access to the western basin of the Mediterranean, thereby making British retention of Malta all but impossible and facilitating the victory of the Axis forces in the Western Desert, and that this would result in Spain and Portugal being drawn fully into the Axis sphere of influence.

The XXXIX Corps was to comprise Generalleutnant Friedrich-Wilhelm von Chappuis’s 16^th Division (mot.) that was to concentrate its efforts on Valladolid in north central Spain, Generalleutnant Hans-Valentin Hube’s 16^th Panzerdivision that was to concentrate its efforts on western central Spain close to the frontier with Portugal Cáceres, and SS-Obergruppenführer Theodor Eicke’s SS Division 'Totenkopf' that was to concentrate its efforts on Seville in south-western Spain.

The XLIX Gebirgskorps was to comprise the Infanterieregiment (mot.) 'Grossdeutschland', the 98^th Gebirgsjägerregiment of Generalleutnant Hubert Lanz’s 1^st Gebirgsdivision, 26 battalions of medium and heavy artillery, three observation battalions, three engineer battalions with as many as 150 'Goliath' remote-controlled mineclearing tracked vehicles, two battalions of Nebelwerfer rocket launchers, and a 150-man detachment of the Lehr-Regiment 'Brandenburg' zbV 800 special forces unit.

German intelligence assessed British artillery on 'The Rock' as 154 pieces including 56 anti-aircraft guns, so the assault force had its normal artillery complement boosted by 50 heavy batteries with 8,500 tons of ammunition, and also the Mörser Karl tracked equipment with a 60-cm (23.62-in) mortar. The German plan called for a crushing artillery bombardment followed by an assault in which the Infanterieregiment (mot.) 'Grossdeutschland' on the right would take the port area and the 98^th Gebirgsjägerregiment on the left would storm 'The Rock'.

'Felix' (i) would be completed by the establishment of batteries of 240- and 150-mm (9.45- and 5.91-in) artillery on the southern shore of Strait of Gibraltar at Ceuta and Tarifa, and by the despatch of two divisions (one Panzer and one motorised infantry) into Spanish Morocco.

The German plan supposed that Portugal would remain neutral, but made provision for a diversion at Cáceres for an advance down the left bank of the Tagus river should Portugal appeal to the UK.

On 12 November, Hitler issued his Führerweisung Nr 18, which stated that 'political measures to induce the prompt entry of Spain into the war have been initiated…The aim of German intervention in the Iberian peninsula (code name 'Felix') will be to drive the English out of the Western Mediterranean.' It also mentioned the potential invasion of Portugal if the British gained a foothold in that country and requested that the occupation of Madeira and the Azores islands group be investigated.

On 5 December 1940, Hitler met with the German high command and decided to request Franco’s permission for German troops to cross the Spanish border on 10 January 1941. It was planned that Jodl would travel to Spain to make preparations for the attack on Gibraltar as soon as Canaris had obtained Franco’s agreement. Accordingly, Canaris met with Franco on 7 December and indicated the importance of Spain’s immediate entry into the war. Franco responded that Spain was simply not capable of supporting the German army because of shortages of food and his country’s crippled infrastructure as it was still recovering from its recent civil war (1936/39). Franco also expressed his fear that a German seizure of Gibraltar would lead to the loss of the Canary islands group and Spanish Africa to British counter-invasions.

On receiving Canaris’s report, Hitler decided that 'Felix' (i) should be cancelled. His disappointment was reflected in a later letter to Mussolini in which he said that 'I fear that Franco is committing here the greatest mistake of his life'.

In the first weeks of 1941, unsuccessful efforts were made by the ambassadors in Berlin and Rome to encourage the Spanish government to change its stance. Franco responded negatively to another request from Hitler, on 6 February, to join the war again by using as a pretext the precarious state of Spain’s economy and army in the aftermath of the civil war. The German foreign minister, Joachim Ribbentrop, told Hitler that in his opinion 'Franco has no intention of ever joining the war.

In February 1941, the Oberkommando der Wehrmacht advised the Oberkommando der Kriegsmarine that in the current situation 'Felix' (i) was out of the question, at least for the time being, as the troops earmarked for it would soon be needed elsewhere.

The British were, of course, all too well aware of both Gibraltar’s strategic value and its vulnerability to attack from the Spanish mainland. On the outbreaks of war with Italy in June 1940, most of Gibraltar’s civilian population had been evacuated to the UK and other parts of the empire, the exceptions being those in vital jobs in the dockyard or who were members of the Gibraltar Defence Force. The garrison was also more than doubled, and the anti-aircraft defences were greatly improved. Work started on a programme to improve Gibraltar’s fortifications, these including a new network of tunnels deep inside 'The Rock' and a system of strongpoints and minefields covering the land border.

In the spring of 1941, the British garrison of Gibraltar’s area of just 2.6 sq miles (6.8 km²) was four battalions of infantry, one regiment of heavy artillery with eight 9.2-in (234-mm), seven 6-in (152-mm) and six twin 6-pdr (57-mm) coastal guns, one anti-aircraft regiment with four 3-in (76.2-in), four 3.7-in (94-mm) and two 2-pdr anti-aircraft guns, one heavy anti-aircraft regiment with 16 3.7-in (094-mm) guns, eight 40-mm Bofors light anti-aircraft guns and radar, one searchlight battery, the 'Special Detachment' of the Canadian No. 1 Tunnelling Company, the Canadian 2^nd Tunnelling Company, and a number of engineer, signals and other units.

A further British defensive countermeasure was the creation of a group of specialist army and navy officers known as the 128^th Liaison Delegation Party, which was to be activated if and when German forces moved into Spain. It had two alternative roles. The initial role would be to provide support to Franco should he decide to resist the Germans and to provide liaison for any British force sent to support the Spanish forces. The second role, in the event of Franco colluding with the Germans, was to demolish Spanish ports and infrastructure and to organise resistance and sabotage with the participation of the Special Operations Executive. That role became pre-eminent later in the war when the group was renamed the Joint Intelligence Centre.