The torpedo used two concentric shafts, this chap seemes to have a certain amount of success...

http://www.pt-boat.com/torpedo/torpedo.html

The model is similar to this one, although as the owner explained to me yesterday, mine is a vastly inferior model made in the mid 90s. Still great to cut my teeth on...

http://www.otwdesigns.com/Seehund/seehund.htm

The magnets I bought have a tractive force of 1.02kg which should be plenty. Found this servo:

http://www.huntersystems.co.uk/acata...o_Control.html

go down to Mega S04/BB 1/4 scale servo, I think it should be powerful enough to pull two of these magnets...do you know if I can run two of these servos off a single channel? Would I need some sort of in-line booster???

Cheers...