Blow Them Up

Meanwhile, at the same time, one hundred and fifty meters below the position of the first Imperial Yamato Fleet, a copy of the Collins Class diesel-electric submarine, His Imperial Ruthenian Majesty's Ship Morzh Class Submarine stealthily trailed the enemy fleet at a speed of three knots

The submarine was under the command of Captain Vasily Aleksandrovich Arkhipov. They are tasked to trail the enemy fleet covertly all the while informing the Ruthenian High Command of their whereabouts. 

The Yamato Empire's current sonar capabilities couldn't detect any noises produced by the submarines except for the wailing of the whales or the fish wagging their tails. It was all thanks to the Stirling engine integrated into the ship, making the ship almost quiet and vibration free, making it hard for the enemy sonar operator to find them.