i don't know if anyone is still looking at this thread but one thing i know that works is bottle rockets. if you launch them parallel to the water maybe a few inches above the water, they will drop in and travel just under the surface and then explode, just like a torpedo. it is really neat and i've done it a few times(can't recall where i was though, cause they are illegal here) they look exactly like torps when they are going under water, its awesome to see.
Jarrod