the vanguard

剑桥词典

the part of an army or navy that leads an attack on an enemy
先头部队，先锋；尖兵
比较
rearguard

a group of people who lead the development of new ideas , or a leading position in the development of something
（思想的）先驱；领先地位
He is in the vanguard of economic reform . 他是经济改革的领头人。
也见 the forefront 返回 the vanguard