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During the Battle of Donatu V in 2244, Bannock devised the flanking maneuver that allowed Federation forces to overcome the Klingons and force them to withdraw. On the following years, Bannock's strategy became known as one of the most brilliant gambits in military history. (TOS - My Brother's Keepernovel: Republic)
There is a possibility that this Excalibur was meant to be the USS Excalibur; however, the events surrounding the Battle of Donatu V as featured in the Errand of Vengeance and Errand of Fury trilogies highlight that the USS Constitution had only recently been launched, and the USS Enterprise was under construction. Therefore, its seems unlikely that this was the Constitution-class Excalibur.