A few years before the outbreak of the One Year War, word of the Principality of Zeon's new "mobile suit" weapons reached the ears of Earth Federation intelligence. Upon launching their "Project V" in UC 0075, the Federal Forces started their own mobile suit development project, and their earliest effort was the RX-75 Guntank. Although it did have a mobile suit body, head and arms, it did not have a mobile suit's walking legs, being mounted instead on a caterpillar-driven tank-like base. It also did not have manipulator hands, and in a sense, the Guntank was more of a tank than it was a mobile suit. However, the Federation did decide to put the unit into mass production. The RX-75 Guntank Mass Production Type was very similar to its prototype predecessor, although the most notable difference was the removal of the expensive and complicated Core Block System. Although the loss of the Core Fighter reduced the pilot's chances of bailing out alive, it did allow the body to be built to perform a "torso twist," thus making the Guntank's upper body able to turn to face different targets while its drive base continued travelling in one direction. The mounts for the shoulder cannons were also made "universal," capable of mounting different types of cannons, weapons or other equipment. Some of these Mass Production Types did serve in the One Year War, particularly as part of the Kojima Batallion in Southeast Asia. Some were refitted for armored recovery and had their artillery cannons replaced by crane arms, and a dozer blade attached to the drive base.