1st Battalion 1st Marines (1/1) is an infantry battalion in the United States Marine Corps based out of Camp Pendleton, California consisting of anywhere from 800 to 2,000 Marines and Sailors, but the number fluctuates depending on the Battalion's mission. They fall under the command of the 1st Marine Regiment and the 1st Marine Division.

http://en.wikipedia.org/wiki/1st_Battalion_1st_Marines