The lowest rung of the Chinese officer command ladder - a 排 (platoon) is ~30 soldiers. 排长 is typically the first post for a fresh military-academy graduate, personal grade 少尉 or 中尉 (second / first lieutenant). Next step up: 连长 (company commander).
grammar
排 here is the military measure for 'platoon' - unrelated to 排 'to line up' (排队) or 排 'row' (一排椅子). Same character, different senses sitting side by side.
