Twenty-seven of the early A models were built. Gradual improvements made during the manufacture led to a new B model, though in reality, there were few differences between the last of the A and the first of the Bs. Most of the early Zaku Is went to training battalions, as Zeon was eager to give pilots experience in the new machines.

Zeon's war plans against the Federation involved destroying space colonies as quickly as possible in the opening hours of a war. Special commando teams were created around the Zaku I. Tactics such as the insertion of poisonous gas, the use of nuclear explosives, and the attachment of rocket motors to move colonies out of their orbit, were created and practiced by these teams. Their deadly effectiveness was shown in the one week war when a quarter of the human population perished.

Shown above is one of these commando units as it appeared in late 0077. They sport a number of modifications to the standard Zaku I, most obvious being the redesigned chest hatch. This MS is wielding the 100mm Zaku machine gun. It was an underpowered and unreliable weapon. Pilots quickly swapped their 100mm guns when stocks of the improved 120mm Zaku machine gun became available.

The MS was initially seen as an anti-colony weapon and early war planners didn't think the Zaku could stand up to Federation battleships. The success of field trials and especially the new tactics pioneered by the Black Tri-Stars led to a re-assessment of the mobile suit. Engineers radically evolved the Zaku and in 0078 a new model, dubbed the MS-06 Zaku II, was produced. It was this MS which saw the majority of combat in the OYW and became the symbol of Zeon's military might.