The front main gun has been improved for a higher rate of fire.
Missiles and torpedos have been changed.
The main guns barrels have been improved.

small changes.

Retrofit V2: LAMS changed slightly, shields weakened, more LAMS nodes, more engines.
First viable version.

V1: Weak armour, 3 main guns, useless LAMS, weak shields, unstable, sank on spawn if not let to sit and charge.
V2: Better armour, better LAMS, expensive shields, stable, sank on LAMS firing more than 6 times.
V3: Good armour, expensive shields, tuned PIDs, sank on LAMS and shields working at once.
Retrofit V1: 2 Main guns, better spoofing, faster, weak 2 layer shields, good LAMS, better engines
(more steam+Redline), more torpedos, better AA missiles, AA simple laser turret.