Atomic Bomb- Each Atomic Bombs costs 10 IPC and only one can be made each turn. When dropped no AA roll is made. Effects: 3 dice of variable damage and one die of permanent damage. The first turn this can be developed is turn 7. Prerequisite: Heavy Bombers technology.
3 dice reduce the income of the player, and a 4th die is permanent reduction. If you A-bomb Germany and roll a 4, the German player gets only 6 IPC from it for the rest of the game and can only place 6 units. You cant get it until turn 7 ( really not possible anyway unless you roll perfectly) and aa guns get no roll against the bomber. Also, you can only drop one per turn.
According to the rules it is a 5th tier technology which requires you to have 4 other technologies in the same category and one of them must be Heavy Bombers.
If you calculate the odds of getting it more or less it may appear on about turn 12-15 as long as you always have a researcher in that category working on it. Most games are over by that time.