Paul Cook -
 I have now finished the X Craft, she is finished  as X 7. Commanded by LT Godfrey Place.
Based on the Darnell/ Metcalfe kit at 42 inches long, she has a main ballast tank controlled by a water pump.

The commander on the deck can be removed for diving, he also holds a flash lamp operated by the Robbe Decoder from the FC 16 radio, power to the main drive which is a 545 motor powered by 6 x Sanyo 3000 mAH cells, the pump which is a Halfords washer pump is powered by an electric flight "forward only" speed controller and 8 x 1850 MAH cells.
This system is known as the closed pump system, as the air pressure build up then surfaces the boat, hence the dive only mode!
Paul Cook
Norwich, Norfolk, UK