Alsos personnel followed close behind the front lines in Italy, France, and Germany, occasionally crossing into enemy-held territory to secure valuable resources before they could be destroyed or scientists escape or fall into rival hands.

The Alsos Mission was commanded by Colonel Boris Pash, a former Manhattan Project security officer, with Samuel Goudsmit as chief scientific advisor.

[6] Following the September 1943 Allied invasion of Italy, Brigadier General Wilhelm D. Styer, Chief of Staff of Army Service Forces,[7] was concerned that intelligence activities related to foreign nuclear energy programs were not being properly coordinated.

He feared that important items might be overlooked unless those responsible were properly briefed, yet at the same time wished to minimize the number of personnel with access to such secret information.

[12] Pash had served as the head of the Counter Intelligence Branch of the Western Defense Command, where he had investigated suspected Soviet espionage at the Radiation Laboratory at Berkeley.

[13] Pash's command comprised his executive officer Captain Wayne B. Stanard, four Counter Intelligence Corps (CIC) agents, four interpreters, and four scientists: Dr. James B. Fisk from the Bell Telephone Company, Dr. John R. Johnson from Cornell University, Commander Bruce Old from the Office of Naval Intelligence (ONI) and the Massachusetts Institute of Technology (MIT), and Major William Allis, originally from MIT although then serving on the War Department scientific staff.

[23] Pash took key scientists into custody and arranged for sites targeted by Alsos, including the University of Rome and the Consiglio Nazionale delle Ricerche, to be secured.

[25] In December 1943, Groves sent Furman to Britain to discuss the establishment of a London Liaison Office for the Manhattan Project with the British government, and to confer over coordinating the intelligence effort.

Working in cooperation with Welsh and Michael Perrin from Tube Alloys, the London Liaison Office consisted of Calvert, Captain George B. Davis, two Women's Army Corps clerks and three CIC agents.

It compiled lists of German scientists of interest and possible locations of nuclear research and industrial facilities, and the mining and stockpiling of uranium and thorium ores.

[34] Meanwhile, the new head of G-2, Major General Clayton L. Bissell, at the urging of Groves and Furman, decided to create a new, even larger Alsos Mission for western Europe in March 1944.

[40] On 5 August, Pash received a secret message from Washington, D.C., reporting that the French physicist Frédéric Joliot-Curie had been sighted at his holiday home at L'Arcouest in Brittany.

Joliot-Curie was at the top of Alsos's wanted list, so Pash and CIC Special Agent Gerry Beatson set out to investigate in the wake of the advancing U.S. Third Army.

[44] The rest of the advance party of the Alsos Mission moved to Normandy in August 1944, where it joined T-Force, a similar formation to S-Force, at Rambouillet, where it was preparing for the liberation of Paris.

[45] An Alsos Mission team including Pash and Calvert reached Joliot-Curie's house in the Paris suburbs on 24 August to find that he was not there, but at his laboratory at the Collège de France.

The next day they reached the Porte d'Orléans where they encountered troops of the French 2e Division Blindée, who were engaged in liberating the city, and came under small arms fire from the German defenders.

A six-man Alsos Mission team set out to secure them, led by Pash and the Assistant Chief of Staff, G-2, at ETOUSA, Colonel G. Bryan Conrad.

Brigadier Edgar Williams, the 21st Army Group's Chief of Intelligence, facilitated the Alsos Mission's detour to Eindhoven, where it was able to interview Dutch scientists.

[59] On 22 November, the U.S. Sixth Army Group notified the Alsos Mission that the capture of Strasbourg was imminent, and it should join T-Force in Saarburg, where it was preparing to enter the city.

[61] Documents discovered in Weizsäcker's office, Fleischmann's laboratory and the Strasbourg Hospital pointed to nuclear activities taking place at Stadtilm, Haigerloch, Hechingen, and Tailfingen.

After establishing its headquarters in Haagen's office Alsos staff uncovered documents concerning secret medical experiments at Natzweiler concentration camp.

[71] On 30 March, the Alsos Mission reached Heidelberg,[68] where important scientists were captured including Walther Bothe, Richard Kuhn, Philipp Lenard, and Wolfgang Gertner.

Scientists captured at Göttingen and Katlenburg-Lindau included Werner Osenberg, the chief of the planning board of the Reichsforschungsrat,[74][75] and Fritz Houtermans, who provided information about the Soviet atomic bomb project.

[76] At Celle, the Alsos Mission uncovered an experimental centrifuge for separating uranium isotopes, the result of work undertaken at the University of Hamburg by a team under Paul Harteck.

As it was in the occupation zone allocated to the Soviet Union at the Yalta Conference, the Alsos Mission, led by Pash and accompanied by Lansdale, Perrin and Air Commodore Sir Charles Hambro, arrived on 17 April to remove anything of interest.

Sir Charles Hambro decided to accompany the Alsos Mission with a British group that included Michael Perrin, David Gattiker, Eric Welsh, and Rupert Cecil.

[87] In a laboratory in a cellar they found a German experimental nuclear reactor shaped like a cylinder and made of graphite blocks, but the uranium and heavy water were missing.

Pash left Hambro in charge, while he led troops of Task Force A to Bisingen, and then on to Hechingen, where 25 scientists were captured, including Weizsäcker, Laue, Karl Wirtz, Horst Korsching and Erich Bagge.

[107] In the end, the Alsos Mission contributed little to the Allied defeat of Nazi Germany, because the German nuclear and biological weapons programs that it had been formed to investigate turned out to be smaller and less threatening than had been feared.

In its appropriation of the accomplishments of European science, the Alsos Mission played a small part in the wartime and subsequent scientific and technological developments that characterized and transformed the postwar world.