So people are leaving out fortress and how it actually works
During only the turn an ancient gear monster is summoned to the field does it negate destruction and targeting effects.
If it’s not the turn summoned whole fortress is on field castle will 🔥 reactor dragon.
"Since this is a Continuous Effect, Ancient Gear Reactor Dragon and Armades, Keeper of Boundaries are not able to prevent it, but the it’s also true that the Field Spell does not negate the attack, which means that, if your opponent has an Ancient Gear Fortress and Ancient Gear Reactor Dragon was Summoned during that turn, then the monster will not be destroyed and the attack will go through."
Correction: Reactor does NOT prevent Stromberg from destroying it, Fortress does. But Stromberg is an EFFECT activation and not a CARD activation, and that's why Reactor (by itself) does NOT.
Effect activation = :/; in the card text for a card that goes into play when the card is face-up.
Card activation = :/; in the card text for a card that is activated as soon as flipped up or from hand.