The biggest issue with torpedoes that small will be buoyancy, what's the point in diving for your torpedo every time you've launched it...?
If you can solve the weight problem than go for it!
Remember to pick a powersource that will give you 30 seconds to a minute runtime, maybe even less, depending on the speed it reaches, to prevent losing the torpedo out of sight.

Let us know how things go.

Regards, Jan.