This ability causes damage to buildings and vehicles and can help capture cities
The Gadget Bomb can be seen as a one-shot ICBM that has enough power to kill an Epic Creature and capture a city. However, using it results in a -90 "Used Nuclear Weapons" negative relationship with all nations and when used on cities, creates useless and irremovable radioactive junk in the place of all of a city's destroyed buildings' slots, making the city useless. The radioactive junk does clear up eventually, but it takes around 6 to 8 in-game hours for it to do so. To use it you have to acquire 4 cities, 16,000 Sporebucks and to have had completed the Tribal stage as an aggressive tribe.
The Gadget Bomb is a very powerful weapon and is probably a better idea to use it on a large fleet of inbound enemies. Another useful way of using it is to use it on a city that is posing a threat to you, but has no value to you, should it be captured. If you don't use the ICBM (Or other Mass Capture Weapon) to finalize a game, or don't have enough money to pay the for the Superweapon, it can be useful to capture the final city, however a warning, the radioactive junk created by the Gadget Bomb carries over into Space Stage as well. It can be seen that the Anti-Matter Bomb is an updated version of the Gadget Bomb. The Gadget Bomb can also be very useful if you want to kill an epic that is too close to your city.
The name is a reference to the name of the first atom bomb ever detonated, which was code named "the Gadget".
Rubbish Piles - http://forum.spore.com/jforum/posts/list/16868.page