I think this makes the most sense if you want to add a house rule for A-bombs (because historically, they were used in the war). They can only be dropped on enemy cities and by bomber, rolling a 5 or lower to effectively destroy the city - not because you could miss but because this new tech might fail. Each city destroyed reduces the number of Victory Cities needed to win the game by one. Mark the destroyed city with the black side of a round marker. Such a rare weapon would only be used to demoralize the enemy, with the goal of surrender.
It would only become possible to discover A-bomb tech starting on turn 5. If you score a research breakthrough and then roll one of the same breakthroughs you rolled in a previous turn, roll again as normal. If on the re-roll you again get one of the same ones you already have, you could choose not to re-roll again but instead discover the A-bomb. That player could then drop one A-bomb per turn (assuming you have a bomber in range of a target city).
This keeps it simple. If this particular house rule has already been devised, sorry, I just got AA50 for the first time, never played any version before.
An Atomic Bomb destroys a city, not a whole country.
This is a good point. One kind of house rule for A-bombs which would substantially affect the game would be to modify the victory conditions, which at the moment only deal with capturing and holding victory cities, to allow for the nuclear destruction of a victory city. I don’t know how this could be translated into victory conditions or player objectives – players who are interested in using A-bombs would have to decide that for themselves – but it’s an idea that might be worth exploring.