Due to the Vulcan government's decision to withdraw from the war efforts, Andorian forces were spread thin in an effort to defend Andorian territories as well as those of its Coalition allies, leaving defenses at the far flung colony world Threllvia IV limited.
The Andorian Imperial Guard vessel Ka'Thelan Krotus was on guard near Threllvia IV when three Romulan Birds-of-Prey ambushed her. During the attack the Romulans tried to take over the Ka'Thelan Krotus with their telecapture system, but the Andorian vessel self-destructed to prevent her capture. The heavily damaged Romulan vessels retreated.
Twenty minutes later the Earth Starfleet vessel Enterprise arrived on the scene and were able to rescue 14 survivors from three escape pods. After an hour of scanning, they were unable to find any more survivors, so they departed the area.
Upon learning that three of his friends and former crewmates died in the destruction of the Krotus, General Thy'lek Shran decided to re-enter into the Imperial Guard's service. (ENT - The Romulan War novel: Beneath the Raptor's Wing)