Kammala wannan jumla: Lokacin da Amurka ta shiga yakin duniya na farko, Hayward ya canza kansa zuwa aiki a cikin tsaron kasa a matsayin colonel na Infantry. Kamar yadda akwai regiments samuwa a gare shi, ya recruited, horar, kuma uniformed da 15th New York Infantry, wani dukan baki masu sa kai regiment. Daga baya aka yi wa wannan rundunar lakabi da Harlem Hellfighters. Rundunar ta isa Turai a cikin bazara na 1917. Janar Pershing, wanda Hayward ya yi aiki a matsayin ɗan takara, ya yi yaƙi da sojojin Faransa a ƙarƙashin sunan 369th Infantry Regiment. Sun yi gwagwarmaya a gaba na kwanaki 191, fiye da kowane rukuni na Amurka, kuma sun shiga cikin
Champagne-Marne, Aisne-Marne, da kuma Meuse-Argonne. An ba Hayward lambar yabo ta "Croix de Guerre" tare da dabino na zinariya da tauraron azurfa da lambar yabo ta Musamman, Marshal Foch da Janar Pershing sun yaba masa, kuma an sanya shi jami'in Legion of Honor godiya ga shawarar Janar Petain. An tattara shi tare da sauran rundunar a watan Maris na 1919.