- You may be looking for the unrelated moon, Delta III.
It was the location of the first joint Borg/Cybermen attack against the Federation in 2368. The planet was overwhelmed in minutes, forcing its Prime Minister to order a planetary evacuation well before Starfleet's defensive task force could arrive. (COMIC: Assimilation²)
- Delta IV at Memory Alpha, the Star Trek canon wiki
- Delta IV at Memory Beta, the wiki that covers all licensed Star Trek works