Groves realized that in the rapidly shrinking postwar military he would not be given any assignment similar in importance to the one he had held in the Manhattan Project, as such posts would go to combat commanders returning from overseas, and he decided to leave the Army.
Groves indså, at i det hurtigt skrumpende militær efter krigen, ville han aldrig få en opgave, som i betydning kunne sidestilles den han havde haft i Manhattanprojektet, da sådanne poster ville gå til generaler, der vendte tilbage fra kampmissioner i udlandet, og han besluttede at forlade hæren.