consisted of three Common Booster Cores (CBCs), each powered by an RS-68 engine. Two served as strap-on boosters attached to a central core. During ascent, all three engines ignited at liftoff, with the central engine throttling down partway through flight to conserve propellant before throttling up again after booster separation.

A distinctive feature of Delta IV Heavy launches was the hydrogen-fueled ignition sequence, which often produced a large fireball that