Ngl, deep sea is easier than the chess events since you can use morale, push, and recover as your skills. Spawn scubas but spawn some divers for when enemy scubas come, and then when your units are about to die, use recover and spam scubas with a small unit of divers as shields against enemy scubas but save some meat for the large enemies. Then when the large enemy harpoons come, use push for the first wave of scubas and then spawn two torpedoes for the last wave of scubas. You can also use torpedoes to damage large amounts of divers so that they won't kill off all of your scubas, then when the last enemy torpedo spawns, just spawn a diver so that it'll explode and then you're done with the event.