1.pressure (when the bomb hits the ground).
2. Timer (When the clock reaches zero an electrical impulse sets off the bomb.
3. Radio. (when the right signal is received by the bomb it does the same as the timer.
The bomb was first invented by the British who used it in WW1 dropping small bombs by hand over enemy trenches.
The bomb was invented with the best intentions of killing and maiming people by tearing them apart with great force however due to the advances of Science we now can put in different wonderfull things like Anthrax, cyanide and Plutonium.
With these little helpers we now have the ability to deliver the most deadly chemical on earth which only takes 1 millionth of a gram to kill you all over world.
The current holders of this weapon have hundreds of kg of it
China, USA, Russia and Great Britain currently have the ability to wipe out the worlds population with a mear 60g of the stuff.
Hiroshima dissapears in a fluffy mushroom cloud and remains uninhabitable for many years.