First Strike
S3, E20: A failed attack on a Replicator armada forces McKay to follow in the footsteps of the Ancients, millennia before, and take a drastic step to save Atlantis from destruction.

S3, E20: A failed attack on a Replicator armada forces McKay to follow in the footsteps of the Ancients, millennia before, and take a drastic step to save Atlantis from destruction.