The Myhr'an planet killer was a large Myhr'an starship, several kilometers in length, capable of causing massive surface damage to planets. In 2372, the Myhr'an planet killer destroyed Starbase Expanse 4, appearing to kill thousands of people in the process. It was also assumed to be used on several Wthaure and other colonies, including a Trookanian colony the USS Marsh responded to a distress call from months earlier. The planet killer, as with other Myhr'an vessels, had some form of cloaking device. After attacking the Altok III colony, the ship engaged this device.