vanguard :

1. (the+S) the leading position at the front of an army or group of ships moving into battle.

2. (C+sing./pl. v) The soldiers who take up this position.

"The vanguard is/are under attack."

3. (the+S) the leading or most advanced position in any course of development.

"In the 19th century Britain was in the vanguard of industrial progress."

in/at the vanguard (of something)

in the most advanced position of development.

“The shop has always been in the vanguard of London fashion trends.”

“The prototype was in the vanguard of technical development.”