USS Diligence (NCC-1956) was a Knox-class frigate on active duty in Starfleet during the late 23rd century. (Ships of the Star Fleet, vol. 1 [revised]) In April of 2281, a task force that included Diligence and the Belknap-class USS Haversham was ambushed by Orion pirates. The bridge of the Diligence was destroyed, killing Capt. Charles Austin and several division chiefs (Star Trek: Shadowstar Station: "The Honored Dead"). Many of the survivors from the Diligence were rotated to other assignments while the ship was in drydock.