The Operation Linebacker II, or Christmas Bombing, was launched by the US Air Force that used B-52s to drop more than 36,000 tonnes of bombs and munitions to shake the Vietnamese “to their core”. B-52s, which was considered the symbol of the US Air Force’s power and believed to be unbreakable, were eventually shot down by Vietnamese soldiers thanks to the unprecedentedly-fierce resistance of Việt Nam's air defence system.