15. Alsos missions engaged German troops as they sought atomic weapons facilities
The Alsos teams advanced ahead of the French Army, behind German lines, supported by a detachment of combat engineers. The missions occurred between April 23 and May 3, 1945. They encountered German resistance, engaging the enemy in firefights as Alsos scientists investigated several atomic research sites. They discovered an intact experimental nuclear reactor which they immediately took apart and shipped back to the American lines. At Hechingen, they captured more than two dozen German scientists, including the long-sought Weizsacker. Tailfingen yielded Otto Hahn, considered by many to be the prize of prizes, as well as several other important researchers. On May 1 they captured Werner Heisenberg, another physicist who had long remained elusive. A German combat group of about 700 men surrendered to the Alsos team on May 3.
As the Alsos team withdrew, Colonel Pash returned with a battalion of American troops, who took the 700 Germans into custody as prisoners of war. The Alsos team retained the captured scientists, and all the Americans withdrew to their own established zones. The French occupied the area May 4, 1945, for the most part, unaware of the activity. What they did know Eisenhower explained to de Gaulle as an overextension during a combat pursuit. Eisenhower also made the decision to treat the captured German physicists and scientists as prisoners of war, but in separate facilities from combat troops and other German civilian prisoners. They were sent to Kransberg Castle, in the German state of Hesse, while plans were made on how to best exploit them and their knowledge. How to use the prisoners became the object of Operation Epsilon.