MOAB - Massive Ordnance Air Blast aka Mother of All Bombs
It is the largest conventional bomb.
Here is a link with some information and a picture.
http://www.globemaster.de/html/moab.html
I would put this as a modern era unit, available through integrated defense to all civilizations as a massive bombard, certain kill explosion. As it is dropped by a C-130, it would be subject to being shot down. If there is a way for it to kill multiple units, and not be a nuke, that would be more correct.
BLU-82B "Daisy Cutter" Dumb Bomb
Vietnam Era predecessor to the MOAB. Here is a link with info and a picture.
http://www.fas.org/man/dod-101/sys/dumb/blu-82.htm
It is similar only smaller in firepower. This would be end of industrial era, advanced flight unit, in my present view. I am thinking how to differentiate their firepower in the toolset, as both should be lethal to full health unit on drop. Both would be in a range that would be factored on a C-130 transport, and despite their graphic appearance would be seen by the game engine as standard air units. I envision their design to be similar to that of the nuclear bomb in the conquests scenario.
My intention for these units is a reworking of civilization 3 to be a lengthier game, heavy in units, with a few more improvements. The primary focus of the mod is to lenghthen the game, slowing down research, changing time scale to months, allowing a more complete enjoyment of each era's units, being unconcerned with win conditions. I play civilization as a simulator, generally without thinking of win scenarios and far past end of game. I am designing the mod to fit that style.