The "Wagner Campaign" was named after him, via which from January to August 1940, 300 tons of strategic commodities, mainly tungsten, were exported from Spain to Germany for war materials use.

With the outbreak of World War 2, the Allies tried to block this sea route trade, and "the Wagner campaign" was devised to organize German merchant ships that were stuck after that in Spanish ports changing their flags and partially subscribing them to Spanish entrepreneurs Juan March.

At the end of the conflict, Wagner, together with the supreme commander of the Kriegsmarine, Hans Georg von Friedeburg, was present and a signatory to the surrender of the German forces in northern Germany at Lüneburg Heath on 4 May 1945 to the British Commander-in-Chief, General Bernard Montgomery.

In 1951 via the Naval Historical Team Wagner authored a paper entitled "A Critique on Vice-Admiral Eberhard Weichold's essay on 'German surface ships—policy and operations in World War II'(promulgated in ONI GHS / 4)".

[4] Two papers known as 'Bremerhaven or Wagner memoranda' were also produced by the Group on the creation of a new post-war German Navy: "Aufbau eines deutschen Marinekontingents im Rahmen deutscher Mitwirkung an der Verteidigung Westeuropas [Establishment of a German naval contingent in the frame of a German involvement in the defence of Western Europe]", the so-called Wagner's memorandum, dated March 1951, and "Ausführungen des deutschen Marinesachverständigen, Konteradmiral a.D. Gerhard Wagner über Fragen des deutschen Marinebeitrages [Explanations by German naval expert Rear Admiral (ret.)