Planet Buster
The Planet Buster was a cannon the size of a moon, used by the Vok aliens in an attempt to destroy the prehistoric Earth.
After the Floating Island was destroyed in a battle against the Predacon forces, a beacon was sent to the Vok. Receiving this beacon, the Vok returned to the Earth and were quite displeased to see that the Beast Wars had completly wrecked their "project". Deeming the entire planet to now be a liability, the Vok revealed their magnum opus, and revealed that the Hollow Moon was in fact a weapon.
The Vok attempted to use this cannon (which Rattrap later dubbed "The Planet Buster") to ignite every Energon deposit on the planet, resulting in an explosion powerful enough to destroy the planet itself!
In order to destroy the weapon, Optimus confiscated a custom-built Stasis Pod (which Tarantulas had built as a means for Blackarachnia and himself to escape from the planet) and loaded it with an explosive.
Optimus's plan was to fly the Pod into the core of the Planet Buster, where the bomb would explode, taking out the Buster with it. Unfortunantly, the Pod itself was a trap, set by Megatron, which revealed itself when Optimus tried to escape from immenent explosion. The plan to destroy the Planet Buster succeeded, but cost the Maximals their leader.
As an unforseen development, the destruction of the Planet Buster created a massive Transwarp Wave. This wave mutated several Transformers into Transmetals, and damaged the stasis pods of others (resulting in the Fuzors and Transmutate).