Kammala jumla mai zuwa: Bayan ya isa Faransa a watan Fabrairun 1918, an sanya Thompson zuwa sashen ma'aikatan leken asiri (G-2) na hedkwatar rundunar sojan Amurka. Daga Yuli zuwa Satumba 1918, Thompson ya kasance mataimakin shugaban ma'aikata na Intelligence a kan ma'aikatan Sojojin Amurka na farko. Ya halarci duka biyu
Aisne-Marne na kai farmaki da Yaƙin Saint-Mihiel. Daga watan Satumbar 1918 zuwa Afrilu 1919, Thompson ya yi aiki a matsayin G-2 don Rundunar Sojojin Amurka ta Biyu, wanda ya hada da aikin yakin basasa na Toul. An gabatar da shi zuwa ga Lieutenant Colonel na wucin gadi a watan Oktoba 1918.