Bombers are redstone and slime block contraptions used by players to drop lit TNT from the sky and were used mostly until the patch of infinite TNT exploit (this exploit allowed to use infinite amount of tnt blocks with bombers)
The first major instance of a bomber's usage on the server was by BastiVC in the Rusher War. 
The bomber design has also been used to clear the hole for Offtopia's Base, The Drain, and several areas in Block Game Mecca.
In the middle of 2018 ,severals bombers was used to dug the 2b2t's Great Spawn Trench
Another more recent usage was by TeamNoTrees to destroy trees and dirt in spawn around november 2019.