Z-Bomb

The Z-Bomb was a doomsday weapon of which by 1986 two or three were available at strategic positions around the Earth. One of them was in the hands of the International Space Command, and their secretary general had the authority to order it used. This particular Z-bomb was located at Snowcap base in Antarctica.

When activated, it caused a nuclear explosion that was said to be powerful enough to split an Earth-sized planet in half.

When Cybermen ships were heading for Earth, General Cutler wanted to use the bomb to destroy Mondas, despite concerns that the radiation effects might kill everyone on the side of the Earth facing the explosion, and that the planet targeted might even turn in a supernova. Cutler considered this an acceptable risk, but his personnel sabotaged the missile.

However, once the Cybermen took control of the base, they planed to use the bomb to blow up the Earth, thus saving their own planet from the effects of the energy transfer between the two worlds. They failed and Mondas was destroyed. (DW: The Tenth Planet)