It's interesting that Russia (Soviet Union) produced a couple of big space rockets which flew very few times (N1 - four unsuccessful liftoffs, Energiya - two su

It's interesting that Russia (Soviet Union) produced a couple of big space rockets which flew very few times (N1 - four unsuccessful liftoffs, Energiya - two successful flights), and USA made a couple of big planes (Spruce Goose, Stratolaunch) which flew very few times (once each).