uwm was provided with X11R1, X11R2, and X11R3.

It was not present in the main clients in X11R4 and above because of ICCCM. Instead of uwm in R4, twm was provided as the default window manager.

DEC provided documentation on uwm with Ultrix, the document (AA-KU50B-TE) is available right here.

uwm on Ultrix 4.5, default configuration	uwm on Ultrix 4.0, custom configuration
uwm on Ultrix 4.5, custom configuration	uwm on Ultrix 4.5, current configuration