From 1938, he was a chief aide to Hermann Göring in the Four Year Plan organization, and headed several high-level diplomatic and economic negotiations before and during the Second World War.

[3] Wohlthat's remit also involved oversight of the German whaling fleet, and he was tasked with planning and preparing for the Antarctic Expedition of 1938-1939.

Preparations took place under strict secrecy, as the enterprise was also tasked with making a feasibility assessment for a future occupation of Antarctic territory.

In February 1939, he negotiated the Rublee-Wohlthat-Plan with George Rublee, U.S. President Franklin Roosevelt's representative to the Intergovernmental Committee on Refugees.

Also, Germany gained the rights to develop additional Romanian oil fields, and was granted lease-free ports on the Danube and Black Sea.

After recently emerging victorious in the Spanish Civil War with the military help of Germany, Spain owed the Reich a great monetary debt totaling approximately $215 million.

Wohlthat's first negotiating session from 12 June to 5 July yielded no results and when he returned in November, war had already been declared.

Franco knew that he would likely face a boycott from the United Kingdom if he tied himself too closely to Germany and he sought to preserve his freedom of action, having already declared Spain's neutrality at the outbreak of hostilities.

[8] Despite initially not attaining all his objectives, Wohlthat's trade agreement eventually bore fruit when, after Germany's successes in the Battle of France, Spain tilted in favor of the Axis powers.

After that, he succeeded in shipping a total of about 240,000 tons of material to Germany via freighters and submarines between 1942 and 1945, though perhaps as much as half never reached its destination due to the Allied blockade.