The various game world guidebooks have explained this detail.
It should be noted that in the Japanese version, the responders are referred to as actually being U.S. Army ACU (Adaptive Combat Uniform) fatigues and equipment, as noted by the IMFDB. Marines deployed to counter the outbreak, and later to neutralize Curtis Miller, are wearing U.S. Artistic License � Military: While most of the weapons used onscreen are accurately portrayed and rendered, the U.S.Armor-Piercing Slap: Claire gives Senator Davis a good one for abandoning Rani.
Hand her a gun, though, and it becomes apparent why she's one of the few survivors of Raccoon City. Per her own dialogue, she's voluntarily demoted herself to pacifism, and would rather look after the civilians than kick ass.
