I also was reading about these subs and the discription reads that in case of radio contact being severed the engines will stop and the unit will blow ballast and rise to the surface? They are talking about a ballast system of sorts? I looked at the Ebay auction that I won, and looking at the pictures it is a new control submarine but he describes is being a Megatech,,, though the transmitter that comes with it needs 8 AA cells and looks like an RC car transmitter with joysticks, I don't know,, confused I hope I get the good one. Thanks for the info once I get under way with my PVC unit I won't keep focusing on this liittle unit don;t mean to wear out a thread.. but I am so new to this submarine stuff it is all learning for me thanks again Tom.