USS Excalibur (NCC-1664)

USS Excalibur (NCC-1664) was a 23rd century Federation Constitution-class starship operated by Starfleet. In 2268, the Excalibur was commanded by Captain Harris. 
In 2268, the Excalibur was assigned to a fleet war games exercise pitting four starships against the USS Enterprise, which was controlled by the revolutionary (but still experimental) M-5 computer. However, when the M-5 malfunctioned, it caused the Enterprise to fire phasers on the Excalibur at full power, when the ship's deflector shields were at minimum intensity. The Excalibur was severely damaged, with all hands lost. It was never towed back to a Starbase.