after the outbreak of world war ii, mcdaniel joined bacher in los alamos, new mexico to work for the manhattan project, where he became a part of robert r. wilson's cyclotron research team. mcdaniel was to have "a crucial role in helping to identify the amount of uranium-235 needed to ... detonate the world's first nuclear bomb". mcdaniel is also noted as having performed the final check on the first atomic bomb prior to its detonation in the trinity test.