I've tried them several times, each with different settings.
I also followed the torpedo down to the warship to see exactly what happens. In all cases, the torpedo went right under the warship keel and did not explode.
Even when the torpedo was set to depth of 1.1 meter (the minimum), it went under the warships keel that is ~3.5 meters deep.
That means that no matter what you set as depth for the electric torpedo, it will travel in depth that is too deep to hit a warship like that (Class A or B)
That also explain why it does hit the big merchants. Their keel is deep enough so that the forced depth of the electric torpedoes does hit it.
So there,
Another bug to fix 
Temujin