Okay, to me some of your examples seem high risk, but still incremental. There was plenty of prior research/innovation/development in those areas that they built upon. But to be fair, I also think that its almost impossible for someone to independently do something 'earth shattering' without building upon other people's work.
You're right, I suppose it's a continuum -- everything is incremental to some degree or other.
The Manhattan project is probably the best example, because there was nothing to build on except "science strongly suggests we could make a bomb out of this; we have no idea yet how to solve the practical issues, or even what all the practical issues are." It was partly incremental in that a much smaller nuclear bomb would still have been useful, but there was definitely a big risk that it just wouldn't work at all.
