The Interplanetary Strategic Alliance Navy (or ISA Navy) is the semi-independent colonial counterpart of the UCA Navy, and is the largest department in the Interplanetary Strategic Alliance; the Navy is responsible for the defense of Earth's colonies and the suppression of any rebellions through space attacks and in the transportation of planetary assault forces. By 2359, the Navy had many advanced ships like the ISA cruisers. However, the ISA Navy is intentionally weaker than the UCA Navy to prevent Vekta from ever rebelling against the United Colonial Nations.
The ISA Navy was founded in the year 2133, and took part in the First Extrasolar War, in which it fought the Helghan Customs Fleet for several years before the UCN arrived, annihilating the Helghan Corporation ships over the planet Helghan. Centuries later, during the Second Extrasolar War, it provided transport and orbital cover for troops fighting on the Helghan surface. A large part of the ISA Navy consisted of Marines, who formed an integral element of naval ship complements and as independent ground forces.
Their main ship-of-the-line is known simply as the ISA Cruiser. These provide the ISA with the persuasive force it requires to keep rebelling planets in line. Both these cruisers' weapons and their ground elements form the basic combat element of the ISA. At the time of the Second Extrasolar War the ISA Navy could deploy twelve Battlegroups to Helghan, each comprising at least 4 warships, principally Cruisers.
During the majority of the First Extrasolar War, the ISA Navy fought many battles with the Helghan fleet, but was eventually forced into hiding after years of fighting and taking casualties, until the UCN reinforced them. The ISA Navy experienced heavy casualties in battle with their enemy during the outbreak of the Second Extrasolar War, due to being phased out in favor of the Orbital Defense Platforms, until they were once again reinforced by the UCN. However, the ISA's fleet had a very successful start to the invasion of Helghan, and took out most of the Helghast's cruisers in the second assault wave on Helghan, without taking a single casualty. Even so, the latter stages of the invasion were marred with the loss of many cruisers over Helghan, including the ISA flagship New Sun. Only two of the ISA's cruisers, from two assault waves, were left after this first devastating counterattack. Performance-wise, The Second Extrasolar War showed the performance of the ISA's ground forces as questionable at best, while their Naval task force very rapidly achieved temporary orbital dominance over Helghan, only being defeated through a deadly combination of a cunning Helghast ambush, the use of boarding parties which negated the ISA's Naval firepower, and an untimely realization of incorrect intelligence right when the Helghast revealed their hidden super cruisers and numerous fighters. Overall, the ISA Navy has, at the very least, proved it's tactical proficiency and worth, and thus seems to be far more effective than the ISA ground forces.Along with the ISA Marines, the Navy also deploy 10 Divisions of Legionnaires.