Some scientists of the late 19th century and early 20th century were without a doubt amongst the most brilliant minds in human history including Albert Einstein, however, there were some theoretical ideas that were shared at the time that just seemed to be rather far-fetched and quite frankly rather laughable to them and for good reason.
As far as ballistics go, the Chinese were the first to invent specialised types of reactive compounds that were used in early pyrotechnics and even early rocketry. This was rather basic chemistry though and this technology grew far bigger over the centuries.
However, the idea that human beings would be able to harvest energy from atoms was unheard of. Even respectable scientists said things like "Anyone who expects a source of power from the transformation of these atoms is talking moonshine" or There is no likelihood man can ever tap the power of the atom. The glib supposition of utilizing atomic energy when our coal has run out is a completely unscientific utopian dream."
Take a look at the video below by the YouTube channel: Veritasium on Why Einstein Thought Nuclear Weapons Were Impossible...