9. The Alsos mission established headquarters in Paris in 1944
As summer turned to fall in 1944, and the Allied armies advanced across France toward the Rhine, the Alsos mission established headquarters in Paris. An extensive search began in the then Allied-occupied areas, for scientists, evidence and records of their work, and physical components of the German weapons programs. In early September the Alsos mission sent a six-man team to join the British forces set to enter the Belgian city of Brussels. Prior to the war, Belgium had been the largest supplier of uranium ore in the world. The Belgian UMHK corporation held a virtual pre-war monopoly on uranium mining and distribution. Its headquarters in Antwerp, and its uranium refining facility in Olen, both offered critical sources of information for the Alsos mission. Incidentally, most of the uranium used by the Manhattan Project came from UMHK, shipped from the Belgian Congo directly to the United States.
The six-man Alsos team traveled to Brussels, where British Lt. Col. David Strangeways provided them with an attachment of armored cars to accompany them to Antwerp. The city had been captured by British troops, but the estuary remained in German hands and the region far from secured. In Antwerp, the Alsos team learned of over 1,000 tons of refined uranium shipped to Germany. Learning of approximately 150 tons at Olen, they arrived there to discover about 80 tons had been shipped to Toulouse prior to the German invasion in 1940. 68 tons of uranium at Olen were shipped to the United States under the direction of General Groves. The Alsos team went to Toulouse to attempt to locate the uranium there. They found only 31 tons, stored in barrels in a French arsenal. It too, was shipped to the United States. The remaining 49 tons have never been found.