A graduate of the Virginia Military Institute and Harvard Law School, Lansdale was commissioned as a second lieutenant in the United States Army Reserve in 1933.

In April 1945, Groves sent Lansdale to Europe, where he worked with the Alsos Mission to secure 1,000 tons of uranium ore from the German Wirtschaftliche Forschungsgesellschaft (WiFO) plant in Stassfurt.

He also participated in the planning and execution of Operation Harborage, in which a special Allied force went deep behind enemy lines, seized 1.5 tons of uranium ingots, and captured a number of German nuclear energy project scientists, including Carl Friedrich von Weizsäcker, Max von Laue, Karl Wirtz, Horst Korsching and Erich Bagge and Otto Hahn.

the Chairman of the National Defense Research Committee, who briefed him on efforts to create an atomic bomb, and charged him with responsibility for counterintelligence at the Radiation Laboratory at the University of California, Berkeley.

He also organised a special counterintelligence group in Washington, D.C., headed by himself, that reported directly to both Strong and Brigadier General Leslie Groves,[6][7] who became director of the Manhattan Project in September 1942.

[14] While waiting for an opportunity to launch this operation, the Alsos Mission learned that uranium ore that had been taken from Belgium in 1944 had been shipped to the Wirtschaftliche Forschungsgesellschaft (WiFO) plant in Stassfurt, which was captured by the 83rd Infantry Division on 15 April.

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

Lansdale had written a legal opinion for the Manhattan Project that it was within the powers of the president of the United States to conclude such agreements with the British without consulting Congress.

[1] Lansdale testified at a 1954 Atomic Energy Commission hearing on behalf of Oppenheimer, who was threatened with loss of his security clearance because of Communist associates.