The X4000-F appears to be a tank-like vehicle meant to be piloted by Aliens. It is roughtly the size of two humans of average height. It has treads on the bottom for mobility, and a dome shaped cockpit on top.
It comes with several weapons and utility devices, including a missile launcher, a cannon of some sort, and a prehensile claw for grabbing
The X4000-F was first seen when the Aliens attempted to capture Joe and Joyce the night after Ruth died. The aliens used its claw to hold Joe in place. The X4000-F was easily defeated when Sal and the rest of Squadron 128 showed up.