Where did the idea come from for the engine?

I felt that if he was going to get this sort of fantastic performance out of the thing, there would have to be very powerful engines of some kind or other, even to the point they might be dangerous to be around. I said, "Well, we better get �em away from the main hall." The other thing is what we called during war a Quick Change Unit. By having the engines out there, if anything is wrong, you can just quickly unhook it and put another in its place.