Unlock 3rd SubClass

[Strike]

So for both my Warlock and Titan after finishing the first quest I unlocked the a 2nd subclass. Now how do i unlock the 3rd one?

[Half-Life 3]

you dont

[Yakumo]

The subclasses unlock through the campaign missions.

[trukr]

Copy paste incoming.
Commander Zavala will send players to Ikora Ray and gain the missions "Riding the Storm," "Stoking the Flame," and "Gazing into the Abyss."

[Kylito]

Ikora in the tower gives you all your light subclass (arc,solar,void) aspects, fragments, supers, and grenades.