[quote=Kadaeux]
No... no it wasn't :pBecause right now we've only got one planet, a propulsion system based on nuclear weapons (While possessed of VAST amounts of thrust/specific impulse) is an absolutely terrible idea if you don't have a spare planet to live on :p
[/quote]

What would have happened:

Orion series commissioned,
Soviets try to counter,
Orion bombs Moscow, US nuclear superiority wipes out SFSR, NATO liberates Warsaw Pact.
China last commie wanna be left.

Sadly, I'm just vastly watering it down, its the jist of how things would have gone in the 1960s/70s.