Front and centre soldier! You're part of UNIT now the Unified Intelligence Taskforce. We are the Earth's best defence against the myriad alien forces who would try to subjugate and conquer our planet. Try they might but they will meet UNIT: a global military force tasked with protecting the planet and researching the alien threat. 

It's not an easy job and even those recruited for their scientific knowledge can find themselves on the front lines of combat against an almost unstoppable foe. It's dangerous violent and not everyone will survive but for the good of the planet we will do everything in our power to protect humanity from extraterrestrial terrors.