Mobile Suit Gundam: Ixtab

Universal Century 0079, The Magellan-class battleship Toutatis tracking a Musai-class in its progress towards Side 2 for a preemptive attack following the Duchy of Zeon's declaration of war, crash-lands in the Island Iffish colony. What they saw there was a landscape wiped out by poison gas. Eventually, they realize Zeon's aim to drop the colony on the Earth. The Toutatis, equipped with a nuclear warhead (hydrogen bomb), attempts to destroy the colony. On the other hand, a Zaku platoon had entered the colony by chance, ordered to subdue and silence dissent among friendly forces.