The Fritz X radio-guided bomb

Considered the "grandfather of smart bombs," the Fritz X was a 3,450-pound explosive equipped with a radio receiver and sophisticated tail controls that helped guide the bomb to its target.

According to the US Air Force, the Fritz X could penetrate 28 inches of armor and could be deployed from 20,000 feet, an altitude out of reach for antiaircraft equipment at the time.

Less than a month after it was developed, the Nazis sank Italian battleship Roma off Sardinia in September 1943. However, the Fritz X's combat use was limited since only a few Luftwaffe aircraft were designed to carry the bomb.

Source: Weapons of WWII magazine