"Some bigger changes have been made to existing units as well like the salvage ships which have also been replaced by Marine Frigates for boarding exercises." - Dan Adams, IGN PC

"And while you may be very confident about sending your capital ship into battle before against such a force, now you understand that, well, that’s all well and good, but if they cripple my propulsion, and the Marine Frigates come in, and they can capture my ship from me." - Alex Rodburg, Brand Manager (Sierra)

"One cool feature is the takeover of an enemy ship by marines, who actually dock the ship you've targeted. The subsystems of enemy ships can be targeted and this will obviously be the primary way of weakening a ship without completely destroying it. Once the enemy ship has been weakened enough, all you need to do is dock your marine frigate onto the ship and watch the leathernecks do their thing." - James Diaz, LoadedInc

It seems very likely that ships must be disabled to a certain point before they may be boarded and captured.

This (U7) is currently my top candidate for the Marine Frigate, but I have no direct confirmation of this. Ah, what the heck... chalk this up as one of those "process of elimination" identifications.

It is armed with a single topside turret.