In June of 1942, Germany began working on a new weapon known as the Vergeltung. Vergeltung means retribution in English. It was built as a response to mass bombings in urban areas of Germany. The British intelligence first became aware of this when a Danish officer discovered an early version of the Vergeltung that crashed between German and Sweden. The Vergeltung is abbreviated to the V-1. The V-1 was pilotless monoplane that was powered by a pulse-jet motor. It carried a one ton war head. The V-2 Flying Bomb was an updated version of the V-1 Flying Bomb. Like the V-1, it also carried a one ton war head. The 14 metres long, liquid-fuelled rocket was capable of super sonic speed and could fly at an altitude of about 50 miles. Because of this, after the V-2 was launched, it couldn't be stopped.