Prior to the war, the Abwehr paved the way for the Anschluss (merger) of Austria with Germany. It also provided strong support to the SDP (Südetendeutsche Partei) of Konrad Heinlein, who aimed at merging the Sudetenland with the Third Reich.
In the meantime however Canaris also tried his utmost to prevent war at all cost. He knew very well that Germany would never be able to win it; according to him the economic and military means were lacking. He was indirectly involved in the planning of a coup d’état against the Hitler regime at the end of 1938, which would be carried out by high ranking officers including Ludwig Beck and his successor as chief of staff Franz Halder. Canaris promised his support and supplied weapons and explosives, he also provided intelligence to Halder. As England and France had agreed to Hitler’s demands by means of the Munich agreement (September 29th , 1938) preventing the war from breaking out, the coup was aborted.
The Munich conference assured Canaris and other military of the opposition that war had been temporarily averted. They decided that the time now had come to thoroughly prepare themselves for a large scale conflict. Canaris did not want this, but he understood that war was unavoidable and if it did break out, he would do anything in his power to make Germany win. From May 1939 onwards, over 1,300 agents carried out reconnaissance missions and sabotage operations in Poland.
When the invasion of Poland finally began on September 1st, 1939, Canaris was appalled by the atrocities committed by the SS and the Einsatzgruppen (Special Action Squads). These units murdered Polish civilians and Jews on a large scale. He once protested against these matters to Generaloberst Wilhelm Keitel personally, stating that: "A war can never be won without taking into account any thought of ethics." His protests fell on deaf ears however and he was told by Keitel that he had to accept the behaviour of the SS as they acted on behalf of the Führer and the Wehrmacht was not responsible. The only thing he could do was to collect incriminating material about the Einsatzgruppen (Einsatzgruppen Art.) and to urge the Wehrmacht to take action accordingly. He had a number of these reports delivered to the Vatican by middle men. By the way, Canaris never undertook anything against the war crimes committed in Eastern Europe by the Geheime Feldpolizei (secret field police) which was commanded by him.War in the West
On January 1st, 1940, Wilhelm Canaris was promoted to Admiral. Canaris maintained contacts with the IRA and various other separist groups in India, Thailand and Irak. He hoped to trigger riots within the British empire through these contacts but at the end of the day, it did not lead to much.
In the meantime Hitler planned a large scale attack on the West (Fall Gelb, operation yellow). Canaris himself had little faith in that campaign beforehand and he considered it suicide. Moreover, he was not the only one to think that way. This led to new ideas about a conspiracy against the regime. The conspirators included the employees of the Abwehr Hans Oster, Hans Dohnanyi and Helmuth Groscurth and a number of officers, among them Franz Halder. These people had already been involved in the plans of 1938. As has been stated, Canaris is supposed to have said several times during this period: "There is not a second to be wasted, Hitler has to go."
Canaris visited the various military headquarters looking for supporters. One of the persons promising support was Generalobers Wilhelm von Leeb (Bio Von Leeb), commander of Heeresgruppe C (army group C), which was deployed opposite the French Maginot line. Most generals however shrank away from a coup as that would weaken Germany too much from the inside and make her easy prey for the Allied forces. Canaris and his associates tried to counter this problem by trying to get in touch with the British via the Vatican in order to come to an agreement should a coup d’état take place. This had little effect because the British for instance had little faith in the German resistance following the Venlo incident. Moreover, Halder withdrew from the conspiracy plans because of the limited support. Canaris therefor had to abandon his plan for a coup, which was a great disappointment to him. He lost his faith in the Wehrmacht generals and would abstain from making coup plans by himself for a long time. He kept protecting the conspirators within the Abwehr however. His role could be characterised as that of a passive leader of the plans.
In the end, Fall Gelb would become a huge success. The Abwehr also performed very well from a German point of view. The service lacked capable agents In France though, making it difficult to gather much concrete intelligence in advance but they succeeded very well in covering up the German plans of attack and make it look like as if the German main attack would be launched in Belgium. The Spezialeinheit Brandenburg (Brandenburg special unit), which was subordinate to Abwehr II in particular was successful. By cunning and misleading actions they succeeded in capturing important bridges and defensive positions in the Netherlands, Belgium and France. Many men of the Abwehr were decorated and Admiral Canaris was praised by the German supreme command as well as by Hitler himself.Negotiations with Franco
In the period October – December 1940, Hitler made various efforts to draw Franco into the war. As Canaris had befriended the general, he was also involved in these negotiations. Discussions were conducted on subjects like the capture of French colonies by Spain and providing a free passage for the German troops to enable them to occupy the British base of Gibraltar. Although Franco made verbal promises to Hitler and indicated that Spain would indeed participate in the war at some time in the future, Franco himself knew that this would never be the case. Spain and her economy were too heavily dependent on the import of raw materials and food stuffs from America and Great-Britain and Germany was not able to take over this role. Moreover, Spain had hardly recovered from the recent civil war. Franco therefore could not plunge his country into a prolonged war. This would only be possible if England would be on the brink of collapse. He did inform Canaris accordingly.
Subsequently Canaris traveled to Southern Europe in order to mediate in the war between Italy and Greece. Canaris however did not succeed in bringing the two belligerents together, also because the Greek parliament was not willing to call an armistice. As a result, Germany launched an invasion of Greece on April 6th , 1941,(operation Marita).