Traditional explosives certainly have their place, but one major preoccupation of WWII ordinance designers was making them even more effective. The British were working on a unique bomb that would contain 30,600 razor-sharp flechettes, each doused in anthrax poison. Because even a scratch would prove lethal, the bombs were lightweight and relatively portable.
If detonated in a crowded area, they could cause thousands of fatalities. The anthrax bombs were never used in combat because against soldiers in cover the majority of the payload would be wasted, but if any terrorist group decided to bring the idea back it could lead to tragedy on a grand scale.