The RX-178 Gundam Mk-II are three prototype mobile suits developed by the Titans, an elite special unit of the Earth Federation forces, in UC 0087. Generally patterned after the original RX-78-2 Gundam, the Gundam Mk-II featured a "movable frame" - wherein weaponry are designed along with the frame of the mobile suit, rather than the mobile suit being only a weapon-carrier. The Gundam Mk-II's design effectively traded armor and weaponry in favor of increased mobility - a very large factor in melee combat common in mobile suit deployment.

When word of these black-and-blue painted Gundams reached the Anti-Earth Union Group, Quattro Bajeena - (Principality of Zeon's infamous "Red Comet") - led a team which infiltrated the Titans' Gryps space colony. With the help of a young boy, Kamille Bidan - son of the Gundam Mk-II's principal designer Franklin Bidan, and a defected Titans officer Emma Sheen, Quattro managed to steal all three mobile suits.

Following the theft of the Gundams, two were sent to Anaheim Electronics to be dismantled and studied, while the AEUG kept the last one in its service, painting over the dark Titans' color and giving it a blue-on-white color-scheme.

The Gundam Mk-II was given to many of the AEUG's best pilots, including the young rookie Kamille Bidan and later former Titans officer Emma Sheen. The Gundam Mk-II, with its antiquated titanium and ceramic composition, limited mobility and weaponry, soon proved ineffective against many of the Titans' new and transformable mobile suits.