The RX-78-6 Mudrock Gundam appeared in Mobile Gundam: Zeonic Front, and Mobile Suit
Gundam: Lost War Chronicles, and is often referred to as the "Murdock Gundam."
Spurred into action by the devastating effectiveness of Zeon’s
mobile suits, the Earth Federation Forces began developing mobile suits
of their own, a project known as ‘Project V.’ Culminating in the
creation of the RX-78-2 Gundam, RX-77-2 Guncannon and RX-75-4 Guntank, the mobile suits proved themselves to be just as devastating to the Zeons. As the One Year War progressed, mobile suit development accelerated, and designers began attempting to combine the best features of the original Project V suits with new technologies being developed by
Earth Federation Forces engineers, including those influenced by Zeon
mobile suits.
The RX-78-6 Mudrock Gundam was one such design constructed at the Earth Federation Forces’ South America Jaburo base. The mobile suit featured a pair of powerful 300mm shell-firing cannons mounted on it’s
backpack, and a pair of beam sabers mounted outboard of the barrels.
The other distinguishing features of the Mudrock were the enormous
number of maneuvering verniers mounted all over it’s body, and the
pair of variable position verniers mounted on the legs, giving the
massive mobile suit unprecedented speed and agility, comparable to
the MS-09 Dom. The Mudrock’s high generator output allowed it to
use a full scale beam rifle, similar in design to the one used by
the RX-78-2. In addition, the Mudrock was capable of using more mundane weapons, such as the Federation’s primer-based rifle, and a 90mm machine gun. All design features taken into account, the Mudrock was more than a match for any contemporary Zeon mobile suit.
The Mudrock first entered combat on November 30, UC 0079, while
still under construction, having been commandeered by a brash young
pilot, Lieutenant Agar. The incomplete Mudrock, with Agar at the
controls, launched in defense of the new Pegasus class warship Blanc Rival. Despite a valiant effort, Agar entered a fierce battle with the Midnight Fenrir, an elite Zeon mobile suit team, and both Mudrock and the Blanc Rival sustained heavy damage. After hurried repairs, the completed Mudrock was assigned to Agar, and sent from Jaburo to the front lines in North America to fight in the battle to retake California Base. The Mudrock entered combat for the last time on December 15, UC 0079. There, Agar and the Mudrock ran afoul of the Midnight Fenrir once again. After a heated battle, the Mudrock was effectively damaged beyond repair by Midnight Fenrir units guarding California Base’s last HLV.

