After the failed attempt at mass-producing nigh-invulnerable Crystallite armors, the bloons resorted to one last desperate option: sending a gigantic Blimp Fleet straight to Grand Monkeyopolis! Together with the Blimp Fleet, the bloons have also managed to steal the monkeys' Shield Generator design, and made a fortress-size version of the thing, the SGM B3, to protect the fleet. The Frontshield is the automated defense system of its core, the Alpha-Epica, so The Monkey must destroy it so his reinforcement can safely go in and destroy the Alpha-Epica, thus destroying the primary defense of the Blimp Fleet.