The United Galaxy Space Force (UGSF) is the main military branch of the United Galaxy. It was formerly known as the United Government Space Force prior to the United Government's reorganization.

At the forefront of the United Galaxy's expansion across the galaxy, the UGSF has seen numerous conflicts ranging in scale. However, during an attack on the planet TRAPPIST-1g, the UGSF was nearly decimated by the efforts of Hester Shaw and the Shivan-UIMS alliance. It was the Doom Slayer who saved the UGSF and gave it a fighting chance against the Shivans and the UIMS, thereby ending Hester's strangehold on TRAPPIST-1.

Many Galaxians, however, were unforgiving for the deaths of John Blade, J.C., Jack Joyce, Beth Wilder, Elliot Swann and Paul Serene and refused to end their state of genocide against the Shivans and the UIMS, sending ships across the galaxy to hunt for Hester and Wren. Even into later years, these Galaxians wished to carry out their oath and completely eradicate the Natsworthy family and the Shivans. One of the missions involved was the destruction of the UIMS vessels Wren Natsworthy and the Hester Natsworthy, as well as many Shivan ships, at the hands of the UGSF vessel B.J. Blazkowicz and their unwitting Shivan allies.