Universe Destroyers

There is a cosmic war raging all around us. The covert team of grey aliens charged with helping humanity to build up their technological capability in order to ensure they can best resist the reptilian invasion force. The humans of Earth must hold off the invasion as long as possible until the greys can build a large enough fleet to fly to Earth's rescue (which will take many decades). And because the greys cannot send much in the way of reinforcements to the humans until the new fleet is b...