A lab upgrade that unlocks missile barrage - which enables you to manually launch a barrage of missiles once per run (which can be increased with the Recharge Missile Barrage lab.
You unlock this lab in Milestones by reaching Tier 8 wave 50.
Missile Barrage - Lab values, costs, and duration (1 level)
By completing this lab, you unlock the Missile Barrage Quantity lab.