Impossible to Destroy Destroyers?

[Drake]

Well I decided to take on a task force.. I was laying hidden, as 3 Destroyers (i belive all were tribal Class) and 3 Southhampton Class (light cruisers?) steamed by me..

I launched 2 torps at the first cruiser, and both hit.. the destoryers closed in as I intented, and as they got close, I launched a torp with the shallowest depth possible....

It went right under the keel, but no hit.. I used an Impact pistol btw, the magnetic dont seem to work that well on small ships.

ive tried redo-ing this many times, and every time it goes under the ship... so whats the deal here?.. is it impossible to sink them?

btw, im using GWX2 if it makes a difference.