Submarine vs fleet ??

Hello,

Can some one help me out understanding a battle.

A fleet of 9x subs llvl 3 is attacking 4x Destroyer lvl 2, 5x cruisers lvl 3 and 3x battleships lvl 2. Right after the attack 2 subs was destroyed and nothing happens with the "enemies" fleet, they lost between 5-10% but that's all..

How does the subs 4 attack points works against those units, because this doesn't seems logic?

Thanks