A smoke bomb or smoke grenade is a bomb that produces a cloud of smoke. It can be used as a toy to make large clouds of colored smoke. It is normally used in the military though. Smoke bombs are used to hide positions and objects from sight behind a thick cloud of smoke. Armies also use smoke grenades to hide soldiers from the enemy. Smoke grenades can be used to mark a spot on the ground (for example, a spot where you want a helicopter to land). Smoke bombs can be thrown or shot. They normally contain a powdered chemical that is ignited. It produces a large cloud of smoke quickly. Then something else starts burning, keeping the smoke cloud thick.