The Marine Stronghold ST1m is a transformable mobile fortress designed specifically for the marines. The origin of the stronghold began as a spontaneous improvisation by arming a Beaver WF4w. Back when Zamaii was still a defenseless village, it was once ambushed by a group of armed extremist. The village engineers temporarily installed 90mm machine guns and 4 cannons on Beaver WF4w. The result of the battle inevitably kickstarted the research into transformable Synchro exoArmors. After further upgrades and enhancements to the Beaver WF4w, the first transformable mobile fortress, Stronghold ST1 was born. Strongholds excel in mid to long range combat, and has proven to be an indispensable part of the national defense force. The Stronghold ST1 was nicknamed 'Quad Eyes' after its 4 giant cannons that the soldiers have come to embrace when counting on artillery support.