Han went to the bottom of the vertical shaft and discovered that this was really a prehistoric civilization launch base. In the deep underground, there were wide rails and heavy transport vehicles carrying interstellar cruise missiles of more than ten kilometers in length.
These kinds of missiles had a built-in transition engine and also a fusion reactor. After being fired, these missiles could hyper jump like starships, attacking targets that were thousands or even tens of thousands of light years away.
As for the warhead carried by the missile, it was a high-energy fusion warhead. Only a few of these interstellar missiles were needed to destroy a planet the size of the moon.
