The engine room could be considered the main lifeline of the ship. Without it, nothing could be done to operate the ship.
Therefore, Leonard realized the sea monsters' attacks were only just an appetizer. The real threat was the internal ship's system that would perfectly bury the ship alive in the sea.
Even if some were to uncover and find the ship later on, much of the evidence would have been destroyed courtesy to the sea monsters.
Leonard failed to calculate this aspect and thought the enemy might strike on the second or third day. Alas, they actually chose to strike immediately—that too in a lightning manner.
"Aren't we going to assist those in the upper deck?" Mirelle was oblivious to the situation and wondered why they needed to rush to the engine room.
For a mage like her, she never had to deal with such a situation. After all, she had the backing of the Mage Association, and not even the Assassin Syndicate would wish to provoke such an entity for no reason.