I te tīmatanga o te tau 1942, ka uru atu a Schrier ki te 2nd Marine Raider Battalion i Camp Elliott, San Diego, i whakatairangahia hei kaitiaki pluton i te Paenga-whāwhā 1942. I te Pipiri 1942, ko ia tētahi o ngā kamupene 2 o Raider Battalion i tukuna ki Midway Island
hei whakapakari i te ope taua ki reira. I uru ia ki te Pakanga o Guadalcanal, a, i uru atu ia ki te 2nd Marine Raider Battalion's epic "Long Patrol" i muri i nga raina hoariri mai i te Noema ki te Tihema 1942. I roto i tenei mahi, i wehewehe ia i a ia ano ma te arahi i tetahi waahanga o tana kamupene kua wehe atu ki te ahuru i muri i te he o tana rangatira kamupene i arahi ia ratou ki roto i te ahuatanga kino. I te timatanga o te 1943, i whakatairangahia ia hei tuarua tuarua i te mara. I muri mai, i tukuna ia ki etahi atu mahi i roto i te whakahaere Raider, penei i te tirotiro me te tirotiro i nga moutere o te hoariri i mua i te taunga mai o nga roopu nui ake. I whakawhiwhia ia ki te Legion of Merit mo tana mahi i te Moutere o Vangunu i te pakanga o New Georgia i te Pipiri 1943. I mahi ano ia i Bougainville hei tautoko i nga mahi hoia i reira. I te Hui-tanguru 1944, i muri i te whakakorenga o nga Marine Raiders, ka hoki ia ki te United States ki te noho hei kaiwhakaako hiko i te Marine Corps Base Camp Pendleton. I whakawhiwhia ia hei rangatira whakahaere mo te Kamupene E, 2nd Battalion, 28th Marine Regiment, 5th Marine Division. I te marama o Hepetema, ka wehe te wehenga tuarima i Camp Pendleton ki Hawaii, hei whakangungu atu. I te marama o Hanuere 1945, ka wehe atu te wehenga tuarima i Hawaii mo te whakaeke me te hopu i a Iwo Jima.