@Boredom:
I laughted a lot reading your answer. Mainly, because i have experienced some of the things you described myself. That Advanced Khaakh Corvete i had managed to capture was destroyed 20 seconds after i gained controll over the ship - by some pesky Khaakh scouts, which i would have killed within seconds, but just haven´t been able to react quickly enough to save both ships.
Therefore i´ve braught a TM + Fighers to a sector for the next time to back me up against those little annoyers. Due to CODEA installed on that TM i could train my Pilots very quick, while beeing really usefull against poping up Clusters ( i was in Zeta Rho sector ).
Concerning the difficulty of capturing: I´ve managed to hack 1xK ( in my HQ sector 4-15, but payed a price loosing 2xM7 + Fighers, so totaly non profitable aqcuisition, but it´s a K! ), 2xG + 2xQ (unknown secotr at the east of Zeta Rho ), 1x Hayabusa ( Atreus Delta ), 1xKariudo ( some border Boron sector ), and a couple of Khaakh Corvetes ( though, it was in previous save ). Except the Kariudo, which i captured on an unintended anti Yaki Patrol ( i do not need another enemy in the neibourhood with M8/M7M... ), all these ships were captured in Unknown sectors. My last attempt to get the "J" failed ( i was hoping the Treser Chest would stay calm long enough, till i can finish my "work", but well... ). The capturing felt not very difficult: maybe because i had no other hostile ships around, and/or because i think i´ve figuered the best way to hack enemy ships ( that small "guide" i wrote in my previous post ).
The Boron Ion Cannon is perfect for hacking of larger ships - M7/M2 (against Corvetes IPG would be better suited, imo): not only it disables shield, makes very moderate damage to hull, but it also really "stunns" the enemy ship - consequently reducing it´s speed and draining weapons energy. I have observed several times the fights between Boron and Xenon navies, and it was quite funny to see, how 3-4 Boron ships were surrounding the remaining capital ship of the Xenon, making it "freeze" at place by firing their Ion weapons ( they just couldn´t finish it effectively

).
The lack of crews on X3 ships will be adressed in Rebirth, till then one has to stick with what we´ve got. Also, modders like Lucike have written some cool scripts to emulate the crews on the ships, at least for the player.
I should continiue my game and will definetly try to cap a "J" or/and an "I", and be back with reports about how challenging it was, if possible at all.
Does anyone know which ship class is concidered "higher" in the ranks M1 of M2? *bump*. Thanks in advance
