the weirdest thing

[Wuss]

imagine the scene,a beatiful sunny morning,calm seas,all is well.
then,ship sighted captain bearing 250.my first contact on this patrol.
I jump onto external camara to check it out and woohoo 2 british merchants.
i plot for an attack on the lead ship hoping to get both of them.
fast foward to in position waiting for the green light.
green light i fire one torpedo,direct hit no boom a bleeding dud
i reposition for another attack and wait for the green light.
green light i fire 2 torpedos this time,both direct hits just under the smoke stack, then WTF
there is no damage what so ever on the ship,i exit the game totally bewildered as to how a ship can take 2 direct hits and chug along as if nothing has happened