Throughout the Cold War, the B-52 was one of the symbols of the overwhelming US air power. The high operational altitude and sturdiness, as well as the terrifyingly large bomb load, make the B-52 the effective strategic and psychological weapon. The threat of a bomber that could fly all the way from the US, drop 32,000 kg of ordnance with impunity was the big puzzle for the North Vietnamese to solve. The Vietnam War was not a conventional war by any mean, so victory for the North depended on its capability to eventually make the losses unacceptable for the US in the long-term. After some deliberations, as the Soviet Union did not want the weapon system that was a cornerstone of the Moscow air defence to demonstrate a poor performance against the B-52, the Soviet Union decided to supply North Vietnam with S-75 missile systems. It earned its fame as a weapon that shot down American U-2s, prompting international geopolitical crisis in both instances. It nearly provoked the thermonuclear exchange between the superpowers when it shot down the U-2 flying over Cuba during the Cuban Missile Crisis. After its introduction, the air war over Vietnam turned into the series of US responses to the new threat and the North Vietnamese adaptations to the US changes in tactics. As expected, Nixon eventually ordered the B-52 to bomb North Vietnam, and during Operation Linebacker II the S-75 managed to shoot down 16 B-52s and damage 9 others. This dispelled or at least damaged the reputation of the invincible US air power. This showdown between the pinnacle of US air power and Soviet air defence systems, and the perceived triumph of the Socialist Camp was probably one of the brightest moments for the Soviet-aligned bloc during the Cold War.