When the UCN was formed, the UCN Defense Force was its military. However, in the midst of expanding colonization and reports concerning allegations of corruption, military inefficiency, and a sluggish bureaucracy, the UCN Defense Force was officially dissolved in 2113 in favor of a more efficient service, with the United Colonial Army being formed thereafter. The UCA Navy was the first service branch of the Army that was formed.
Unlike the Interplanetary Strategic Alliance which relies on local funds from their respective systems to function, the UCA receives funding directly from the UCN. This arrangement provides them with access to more resources and firepower than any of the typical ISA branches. The UCA and its Navy possesses weapons, training, and technology far beyond the level of individual ISA commands. The ISA was created to provide defense for Earth's colonies to prevent the UCN from spreading its forces too thin. To prevent any of the colonies from ever rebelling against the UCN, the ISA forces are kept intentionally weaker than their UCA counterparts.