Question

Which caused the US army to take over atomic research in the early 1940s?

Answer 1

The U.S. entry into WW2

Answer 2

The right answer is The US entry into World War II. Th agencies that later on developed Manhattan project were formed in 1939. U.S. intelligence agents reported that german scientists were working in a nuclear weapon. So the actual project started in 1942 under the command of Colonel Leslie Groves.