Tuhia tētahi tohutoro mō tēnei wāhanga - Ko te tama a tētahi tohunga o te ope taua o U.S., i noho a Groves i ngā pou hōia i tōna tamarikitanga. I te tau 1918, i mutu ia i te tuawha o tana akomanga i te U.S. Military Academy i West Point ka tukuna ki roto i te U.S. Army Corps of Engineers. I te tau 1929, i haere ia ki Nicaragua hei waahanga o te haerenga ki te whakahaere rangahau mo te Canal Inter-Oceanic Nicaragua. Whai muri i te ru o te tau 1931
, I tangohia e Groves te punaha tuku wai o Managua, na te mea i whakawhiwhia ki a ia te Tohu Perehitini mo te Tohu o Nicaragua. I haere ia ki te Kura Whakahaere me te Kaimahi Nui i Fort Leavenworth, Kansas, i te 1935 me te 1936; me te Whare Wananga o te Army War i te 1938 me te 1939, i muri mai ka tukuna ia ki te Tari o te War General Staff. I whakawhanakehia e Groves "he ingoa hei kaimahi, he taraiwa, me te kaitiaki mo te mahi" a i te tau 1940 ka noho ia hei kaiawhina motuhake mo te hanganga ki te Quartermaster General, i whakawhiwhia ki te tirotiro i nga waahi hanga me te tirotiro i to raatau ahunga whakamua. I te marama o Akuhata o te tau 1941, i whakaritea ia ki te waihanga i te whare tari nui mō ngā kaimahi 40,000 o te Tari o te Pakanga, ā, i te mutunga ka noho hei Pentagon.