you know I may have a solution for this problem,

I fly R/C model helicopters, and one that I recently bought is a micro helicopter called the zoom400, it has a micro gyro, now two of these could be fitted into a torpedo, one on each axis, not only this but protech have released some extremly small servos and recievers, which could also be fitted, and with the new lipo battery packs (not too sure about that, you would have to be very careful about water proofing it, or the torpedo could explode) you could make a very small cell to power a motor from the tail of an eco-picolo (very small) all this would make a gyro stabilised torpedo, which could be steered, talk about possibilities