Cika wannan jumla: Catlin ya kammala karatunsa daga Kwalejin Yaƙin Soja wata ɗaya bayan ɓarkewar Yaƙin Duniya na ɗaya. Daga baya, an sanya shi a matsayin mai kula da sansanin horar da sojan ruwa na ƙasashen waje a Quantico, Virginia. A watan Oktoba 1917, an aika Catlin zuwa Faransa a matsayin kwamandan kwamandan na 6th Marines. Daga Yuni 1-6, 1918, Rundunar ta 6 ta ga aikin a cikin layin gaba daga Paris-Metz Road ta hanyar Lucy-le-Bocage zuwa Hill 142. A ranar 6 ga Yuni, 1918, tare da rundunarsa suna kai hari
Bois de Belleau, an ji masa rauni a kirji da wani maharbi kuma an kwashe shi zuwa asibiti washegari. Wannan shi ne karo na farko da aka ji masa rauni a shekara 28 da ya yi yana aiki.