When it became apparent that the newcomers had hostile intentions, Captain Leicester reacted rashly. Believing the GTVA warships comparably armed to his own Karuna, Leicester engaged the Orestes while calling for the 3rd Fleet to respond. He promptly found his ship gutted by the Orestes' plasma beams - the first occurrence of a tactical nightmare that would plague the UEF for the rest of the war.

Calder deployed four frigates to the node but wisely held back his destroyer, the Toutatis. The loss of a second frigate to beam fire from the Orestes convinced Calder to avoid committing the rest of his assets, and his ships retreated, leaving the node uncontested. Meanwhile, the Council of Elders had gathered for an emergency meeting and authorized unlimited defensive action by the military. In retrospect, if the UEF had attacked at this point, victory would have been nearly assured - the Temeraire, Duke, Labouchere, and Miranda were all out of action due to mutiny and other vessels were operating at degraded crew levels.

At this time only two hours had passed since the arrival of the Orestes in Sol. Unbeknownst to the UEF, widespread mutiny was underway amidst the 14th Battlegroup. Some ships defected wholesale, command crews intact. Others were rendered inoperable by onboard sabotage. Had the UEF pressed its advantage at the moment, they might have captured the node (if only temporarily). However, Calder, Netreba, and Byrne were still trying to deduce the capabilities and motives of their opponents, and most of their warships were still loading up for combat at this time.

Two hours later, the Fourth Fleet began its transit into Sol. The 13th and 16th Battlegroups, under the GTD Meridian and GTD Requiem, consisted largely of Capella-era warships, but their Deimos and Hecate combatants - if lacking in the overwhelming shock power of the newer warships - were an easy match for everything in the UEF arsenal. These ships relieved the remaining warships of the 14th Battlegroup and plans were drawn up to assault Neptune.

Although their available assets included two destroyers and multiple corvettes, these vessels were not committed simultaneously. Both GTVA and UEF military doctrine recognized that a warship in reserve was more powerful than one in the field - capable of jumping in and attacking a committed enemy from a weak direction. Moreover, broad deployment of capital or fighter assets left rear-area targets open to attack, including (in this case) the Delta Serpentis node itself. For this reason, both sides committed no more than six or seven warships to an engagement at one time, a policy that would continue for the remainder of the war.

The 13th's initial assault on Neptune was repelled. While the defending force, two frigates and four cruisers, was annihilated by beam fire, the UEF fighter corps ripped apart the 13th's screen and close-assaulted the GTD Meridian with gunship-mounted weapons, demonstrating the UEF's main advantage over its GTVA counterparts. The Meridian withdrew, losing a Deimos escort in the process.