The Battle between I-401 and Takao where the I-401 reveals to Takao it's secret weapon, a Super Gravity Cannon.
The Battle of Yokosuka Bay between the I-401 and Hakugei 3 against Kirishima and Haruna. Kirishima and Haruna batters the Hakugei with their attacks until the I-401 arrives to rescue them. Later, Kirishima and Haruna combine their ships and trapped the I-401 under their gravity field and prepare to fire their combined Super Gravity Cannon. Just when it seems the I-401 last ditch attack to stop Kirishima and Haruna fails, it turns out to be a distraction to allow the Hakugei fires a Corrosion Torpedo into their Super Gravity Cannon, causing a chain reaction that destroys both ships. Hakugei gets the honor of being the first human ship in history to defeat not one but two the Fog ships.
Haruna and Kirishima(With a little last minute assistance from Iona) proving a Mental Model doesn't need its ship to kick copious ass in episode 6.
Episode 11. Iona completely obliterates a fleet of 22 Nagara-class light cruisers with a mixture of her Wave Motion Gun and missile barrage.
Kongou doing the same in her Death Star form to the American Fog fleet. Her version even has a different look to it, appearing more like two interwining twisters than a big laser. Awesome and absolutely terrifying!