A fire support base was originally a temporary firing base for artillery, although many evolved into more permanent bases. Their main components varied by size: a typical FSB usually had a battery of six 105 millimeter or 155 mm howitzers, a platoon of engineers permanently on station for construction and maintenance projects, at least two landing pads for helicopters (a smaller VIP pad and at least one resupply pad), a Tactical Operations Center (TOC), an aid station staffed with medics, a communications bunker, and a company of infantry serving as the defense garrison. Large FSBs might also have 2 artillery batteries, and an infantry battalion.