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Gundam

Frontier IV

Side 4 colony cluster invaded by the Crossbone Vanguard in UC 0123.
Jenxi Seow Published 28 Jan 2026 Updated 28 Jan 2026
Frontier IV

Frontier IV (フロンティアIV, Furontia Fō) was a colony or colony cluster in Side 4 (Frontier Side) in the Universal Century. In March UC 0123 it was invaded by the Crossbone Vanguard as part of Cosmo Babylonia’s campaign to seize territory from the Earth Federation. The invasion and the resistance led by Seabook Arno and the F91 Gundam form the backdrop of Mobile Suit Gundam F91.

Role in F91

The Crossbone Vanguard under Iron Mask launched a surprise attack on Frontier Side, with Frontier IV as a key target. The assault overwhelmed Federation defences and placed the colony under Cosmo Babylonia control. Dorel Ronah directed the invasion of Frontier IV, while civilians including Seabook Arno and Cecily Fairchild were caught in the conflict. The Space Ark and other refugee vessels evacuated civilians, and resistance centred on the F91 Gundam and the Strategic Naval Research Institute development programme.

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