You have to sink 4 enemy ships in a single battle, and your reward for doing it in Japanese ships is the Konigsberg, and in American, the Ognevoi.
Cue using cruisers, and deliberately targeting low-health ships and DD's with continuous fire from main guns.... now who'd do a kill-stealing thing like that eh?
Each ship also comes with a free commander with 3 points to spend, and you'll get to keep the commander and his XP for each of the relevant nations.
Soviet DD is a 'gun' DD, with torps really as emergency weapons - even being tier 6, it has only 4km range on the torps, so they're for that 'aaarrrgh' moment when a CA or BB pops around an island and surprises you! The guns have a decent range, 2x twin 130mm mounts, but which fire at 12 RPM so they can get lots of shots out, and its ridiculously maneouverable so I was at one point making a BB waste all its' fire at me, missing every shot, while it got smashed by other ships.
The Konigsberg is a nice all-round cruiser, torps are 6km range and it has 2x triple launchers on either side. The guns are 3x 150mm triple turrets, firing at 8 RPM (more if you upgrade commander) and can throw out to 16.5KM, so it's ideal for staying at range and keeping enemies back from the rest of your team.
Shame we won't get to keep the ships after the 19th Oct though.