The Zaku Cannon was developed out of the Zeon's MS-06J-12 Project, which was to build an anti-aircraft Zaku II unit. That project was scrapped when the Zeons learned of the Earth Federal Force's close-combat RX-78-2 Gundam and their mid-range fire support RX-77-2 Guncannon. Thus, the scope of the project changed from anti-aircraft mobile suit to an anti-mobile suit and mid-range support unit.
The Zaku Cannon was based on the Zeon's highly successful MS-06F Zaku II design. This new model featured a powerful 180mm cannon mounted on the right shoulder, the same cannon size as the Federation's RX-75-4 Guntank. It could even be refitted with a MS-06J Zaku II Ground Type's standard backpack by removing the K-Type backpack and cannon. The Zaku Cannon also featured a 360 degree camera eye for improved vision and target acquisition. Lastly, the mobile suit had more powerful thrusters placed in its legs to overcome its increased mass. However, The Zaku Cannon suffered from poor balance due to the large cannon's recoil. This problem was significant enough to cancel its production by the Zeon Military Force after a production run of only nine units.
Nine prototype units are constructed at California Base, and this squadron of Zaku Cannons are led by Ian Greydon in defense of the base until the end of the war. Greydon's own Zaku Cannon sports a custom twin-antenna head that comes to be known as the "rabbit type." A handful of other Zaku Cannon units also turn up in other theaters of the Earthside war, including Southeast Asia and Australia.
In U.C. 0087, the Earth Federation picked up the designs. After the costly battle with the Delaz Fleet, the Federation's new and powerful mobile suits had been destroyed. They needed very cheap models to replace the advanced mobile suits that had been lost (the Titans taskforce was using up a great deal of the Federation's money for the military). Thus, the Federal Forces filled their ranks with a few of the old Zeon designs, including the MS-06K Zaku Cannon, to supplement their forces.
In the assault of Torrington Base in U.C. 0096, the Zeon remnants deployed at least one Zaku Cannon.