JF Ptak Science Books Post 1753
Leonardo understood "big", especially when it came to weapons, and he understood what the concept of 'big" meant to adversaries and enemies of the folks with the "big" weapon--a bit of psych-ops in the mid-Renaissance by the High Renaissance man.
Leonardo's crossbow (drawn around 1486) should have worked. He certainly understood the idea of stored power in his many drawings--bent and twisted and torqued wooden arms and such--and the concepts of enormous potential is certainly reeking through-and-through this fantastic weapon. The bow itself seems certainly like a laminated object, adding to its strength via flexibility, the giant bow-string drawn back by a very considerable worm and gear, the whole of which is set to give flight to a large stone more so than an arrow. And that stone was supposed to be able to be delivered to its target over and over again, with minor adjustments, which would have placed it head-and shoulders above cannons, whose recoil made it really quit impossible to re-aim the instrument with any accuracy at the same target over and over again. The main compliment of the crossbow, then, was reproducible accuracies. (In this vein it is interesting to recall "Operation Crossbow", a Combined Bombing Operations during WWII that took place in 1943 and 1944 against the Nazi installations for the V-2 and V-3 weapons--a directed effort to remove a threat which was even more "precise" (if by "precision" we mean marginally guided weapons loaded with high explosives).)
The "atomic" part of the title of this post is I know far from the mark of being metaphorically correct--the scale isn't anywhere near being accurate. Offhand to have an "atomic" crossbow in relation to a nominally normal crossbow in similar scale of the Fat Man weapon in scale with an "average" 500-pound bomb (40 million pounds in relation to 500 pounds) the atomic crossbow would need to be miles wide.