Heist of the Avenger Prototype
The heist of the Avenger Prototype involved the defection of Lieutenant Alexander McCarthy to the Vasudans in 2335.
Acquisition of the Prototype
The Avenger prototype cannon somehow fell into the hands of the Vasudans. It is possible that McCarthy arranged this in preparation for the delivery of the plans to Vasudan Command (Scenario A), but it is also possible that the Vasudans managed to acquire the plans from the Terrans on their own (Scenario B).
Terran Intelligence detected unusual activity at the depot and the Galatea was assigned to capture it. Although Intelligence may not have known that the depot was storing the prototypes, they suspected the depot was militarily significant. During the mission, the GTT Omega removed the plans from the depot before the GTA could completely secure the area. It is not known whether McCarthy was actually aboard the Omega at this point, but it is known that he arranged this heist.
Interpretation of this heist follows from the first. If Scenario A is true, then McCarthy's removal of the plans was simply ensuring that his arrangement did not fall apart and that delivery of the plans to Vasudan Command was still possible. If Scenario B is true, then McCarthy seized the opportunity provided by the commotion at the depot to steal the plans with the intent of returning it to the Vasudans.
Whatever the case, arranging for the GTT Omega to steal the plans right out from under the noses of the GTA during a GTA capture operation was a risky move, and if the GTA did not know about McCarthy's objectives before then, they would certainly have known at that time. If Scenario A is true and if the GTA had not conducted the capture operation, then it is entirely plausible for McCarthy to have gotten away with it.
Recovery of the plans
Intelligence became aware of McCarthy's plot and was able to capture one of McCarthy's accomplices. Between this and the information gathered from Vasudan agents under Terran control, Intelligence was able to learn a great deal about McCarthy's plans. The Galatea was assigned to lead an attack on McCarthy's forces and was successful in capturing McCarthy, his Vasudan contact, and the stolen Avenger prototype. This operation was the 242nd Suicide Kings' first mission and involved the use of the new Valkyrie-class interceptors.
- See also: The McCarthy trials
McCarthy's motives were apparently more than simply financial; he knew that the attack on Ross 128 and what it entailed was far more of a concern than the war against the Vasudans. Perhaps he hoped that delivering the Avenger to the Vasudans would to fight on an equal playing field with the Terrans would improve their odds against the Shivans.
It is likely that history exonerated McCarthy's actions, especially considering that the GTA eventually shared the Avenger with the PVN anyway. We know from FS2 that the McCarthy trials were well-publicized, so it is likely that the trials took place after or during the Great War and were quite dramatic. There were probably a great many questions raised about loyalty to the GTA vs. acting in the best interests of the Terran and Vasudan species.